The Promise Fulfilled
Text: Genesis 21
Core Idea: Our God is the God who fulfills His promise, refines His people, and extends His blessing. Then, let’s learn to wait faithfully, obey fully, and live beautifully for His glory so that the world will know that He alone is worthy of our worship.
INTRODUCTION
Good morning, Lighthouse. I want to welcome all of you, but especially our Tugboat and Anchor friends, as they’ll be joining us for the whole service today. To help our children engage a little more, we’ve been following their curriculum during these joint services – but since they’re also going through the Book of Genesis, I thought it would be good to continue from where we left off last Sunday. If you remember, in Chapter 20, we saw that Abraham’s repeated failure once again threatened the promise and placed Sarah in danger, but God did not allow his sin to undo what He had planned – He stepped in to rescue her and protect His promise. So, if Chapter 20 was about God protecting His promise in grace, today’s passage is about God fulfilling His promise in power because here, we’ll finally witness the birth of Isaac. Then, with that in mind, please open your Bibles to Genesis 21 – and I’m going to invite Ellie, Leo, and Noah to come forward so that they can read the passage for us.
1 Now the LORD was gracious to Sarah as He had said, and the LORD did for Sarah what He had promised. 2 Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him. 3 Abraham gave the name Isaac to the son Sarah bore him. 4 When his son Isaac was eight days old, Abraham circumcised him, as God commanded him. 5 Abraham was a hundred years old when his son Isaac was born to him. 6 Sarah said, “God has brought me laughter, and everyone who hears about this will laugh with me.” 7 And she added, “Who would have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.” 8 The child grew and was weaned, and on the day Isaac was weaned Abraham held a great feast. 9 But Sarah saw that the son whom Hagar the Egyptian had borne to Abraham was mocking, 10 and she said to Abraham, “Get rid of that slave woman and her son, for that woman’s son will never share in the inheritance with my son Isaac.” 11 The matter distressed Abraham greatly because it concerned his son. 12 But God said to him, “Do not be so distressed about the boy and your slave woman. Listen to whatever Sarah tells you, because it is through Isaac that your offspring will be reckoned. 13 I will make the son of the slave into a nation also, because he is your offspring.” 14 Early the next morning Abraham took some food and a skin of water and gave them to Hagar. He set them on her shoulders and then sent her off with the boy. She went on her way and wandered in the Desert of Beersheba. 15 When the water in the skin was gone, she put the boy under one of the bushes. 16 Then she went off and sat down about a bowshot away, for she thought, “I cannot watch the boy die.” And as she sat there, she began to sob. 17 God heard the boy crying, and the angel of God called to Hagar from heaven and said to her, “What is the matter, Hagar? Do not be afraid; God has heard the boy crying as he lies there. 18 Lift the boy up and take him by the hand, for I will make him into a great nation.” 19 Then God opened her eyes and she saw a well of water. So she went and filled the skin with water and gave the boy a drink. 20 God was with the boy as he grew up. He lived in the desert and became an archer. 21 While he was living in the Desert of Paran, his mother got a wife for him from Egypt. 22 At that time Abimelek and Phicol the commander of his forces said to Abraham, “God is with you in everything you do. 23 Now swear to me here before God that you will not deal falsely with me or my children or my descendants. Show to me and the country where you now reside as a foreigner the same kindness I have shown to you.” 24 Abraham said, “I swear it.” 25 Then Abraham complained to Abimelek about a well of water that Abimelek’s servants had seized. 26 But Abimelek said, “I don’t know who has done this. You did not tell me, and I heard about it only today.” 27 So Abraham brought sheep and cattle and gave them to Abimelek, and the two men made a treaty. 28 Abraham set apart seven ewe lambs from the flock, 29 and Abimelek asked Abraham, “What is the meaning of these seven ewe lambs you have set apart by themselves?” 30 He replied, “Accept these seven lambs from my hand as a witness that I dug this well.” 31 So that place was called Beersheba, because the two men swore an oath there. 32 After the treaty had been made at Beersheba, Abimelek and Phicol the commander of his forces returned to the land of the Philistines. 33 Abraham planted a tamarisk tree in Beersheba, and there he called on the name of the LORD, the Eternal God. 34 And Abraham stayed in the land of the Philistines for a long time.
Thank you, friends, for reading the passage for us. And children, I hope you enjoyed that video – summarizing the story of Abraham so far. Now, I’m sure you noticed that this chapter contains three different stories: the birth of Isaac (v. 1-7), the casting away of Hagar and Ishmael (v. 8-21), and the treaty with Abimelek (v. 22-34). At first glance they might seem unrelated, but together they show that God has been faithful to every part of His original promise in Genesis 12:2-3 – this is what God said: “I will make you into a great nation, and I will bless you [fulfilled through the birth of Isaac]; I will make your name great, and you will be a blessing. I will bless those who bless you, and whoever curses you I will curse [reflected in the sending away of Ishmael]; and all peoples on earth will be blessed through you [revealed through the covenant with Abimelek].” In other words, Genesis 21 is not simply the story of Isaac’s birth – it’s the story of a faithful God who keeps His word. Yet as we’ll see, the fulfillment of God’s promise doesn’t make life easier for Abraham. God’s faithfulness continues, but so does His refining work. Three points:
· GOD FULFILLS HIS PROMISE
· GOD REFINES HIS PEOPLE
· GOD EXTENDS HIS BLESSING
1) GOD FULFILLS HIS PROMISE
After 25 years of waiting, after all the buildup and tension, you would expect a long and detailed description of Isaac’s birth – a moment of celebration, music, and joy. But instead, the author records it in just a few short verses. And that’s intentional because the focus isn’t on how Isaac was born, but on who made it possible. Verse 1, “The LORD was gracious to Sarah as He had said, and the LORD did for Sarah what He had promised. Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him.” Three times in two verses, the writer emphasizes that God did it. Not Abraham, not Sarah, not luck – but the Lord Himself. In other words, this is not a story of human achievement – it’s a story of divine faithfulness. Now, let’s pause and feel how incredible this moment really is because Abraham was one hundred years old, and Sarah was ninety. And she didn’t just give birth – she nursed and raised a baby at ninety years old. Think about that. From every human angle, this is impossible. But our God is the God who makes the impossible possible. So, even though Abraham and Sarah’s bodies were as good as dead, the God who spoke light into darkness spoke life into their barrenness.
Now, Abraham’s response shows how much his faith had grown, for he obeyed immediately – two things. First, he named the boy Isaac as God commanded in Chapter 17, and second, he circumcised him on the eighth day, as God commanded. If you think about it, this couldn’t have been easy, considering that he probably never had the experience of circumcising an infant. Ishmael was thirteen when it happened. So, can you imagine how difficult it would’ve been for Abraham to inflict pain on his baby son – the one whom he had waited for so long? And yet, Abraham obeyed – he chose to trust God’s Word more than his own emotions. This is important to point out because it shows that Abraham’s waiting was not wasted. God was using those 25 years to teach him how to trust because faith doesn’t grow in comfort – it grows in waiting. And what came from that waiting was joy. If you remember, back in Chapter 18, Sarah laughed when the visitor said, “By this time next year, Sarah will have a son.” But this was a cynical laughter of doubt, for it seemed impossible – and yet, this time, it was a laughter of joy and delight, for what she only dreamed about happened. Verse 6, “God has brought me laughter, and everyone who hears about this will laugh with me. Who would have said to Abraham that Sarah would nurse children?” In other words, who would’ve thought this was possible? Who would’ve thought a barren woman in her nineties would be nursing a child? Who would’ve thought the laughter of cynicism would turn into the laughter of joy? Who would’ve thought God could take all those years of waiting and weave them into a testimony of grace? She would’ve never thought this was possible – and yet, that’s exactly what God did for her.
And maybe that’s what God wants you to remember today, because we all face moments when faith feels foolish. We look at our lives and think, “There’s no way.” No way that relationship can heal. No way that heart can change. No way that broken situation can be redeemed. But the same God who fulfilled His promise to Abraham can fulfill His word to you. The same God who opened Sarah’s womb can open what seems closed in your life. Let’s be honest: Sometimes the hardest thing to do is hope because to hope often means to let go of control. It makes us vulnerable. And we can’t help but ask: “What if God doesn’t come through? What if this was just wishful thinking?” So instead of growing in anticipation, we protect ourselves by lowering our expectations – by becoming cynical. We stop praying for the impossible and start settling for the manageable. In fact, we justify ourselves by calling it being “realistic” – but it’s actually just fear in disguise. We stopped hoping because we didn’t want to be disappointed. But, friends, faith isn’t naïve optimism – it’s confident dependence on a faithful God. Faith says, “Even if I can’t see how, I know Who.” Then, as you reflect on the past faithfulness of God today, I pray that your heart would echo Sarah’s confession – “Who would have thought?” Who would’ve thought God could still use someone like me after all the mistakes I’ve made? Who would’ve thought the season I dreaded would become the season that grew me the most? Who would’ve thought He could provide when I saw no way forward? Who would’ve thought God could heal that relationship I thought was too far gone? Who would’ve thought my family dinners could turn into moments of worship again? Who would’ve thought God could bring so many different people together and make us one body? Who would’ve thought God could take our small church and make it a place of light and life? In fact, just think about the implications of the gospel: Who would’ve thought God would send His one and only Son to rescue sinners like us? Who would’ve thought a cross, a symbol of death, would become a sign of hope? Who would’ve thought God would turn betrayal into salvation, suffering into redemption, and death into victory? Who would’ve thought the same power that raised Jesus from the dead now lives in us? Who would’ve thought people once far from God could be called His sons and daughters? This is what our God does – turning doubt into delight, waiting into wonder, and impossibility into testimony. Alan Stibbes wrote, “The birth of Isaac was unquestionably an outstanding event in Abraham’s life. It was both a crowning achievement and a new beginning. It happened when he was one hundred years old. None of us can therefore say we are too old, or that it’s now too late, or that we have already waited too long for God to do new things for us and with us. What we need to learn from Abraham is not to be dismayed by the natural hopelessness of our condition and circumstances but to find sure and unfailing hope in God – in His ability, in His words of promise, in His covenant pledges, in His faithfulness, and in His certainty to do as He said.” Abraham and Sarah waited 25 years, but not one of those years was wasted. God used every moment to shape their faith and show that His promises rest not on human strength but on divine grace. Then, as you reflect on the One who is faithful, I pray that you’ll learn to believe again, to hope again, and to laugh again, for this is the joy that erupts when faith becomes sight. And if you’re ever doubtful, He will make that possible in your life.
2) GOD REFINES HIS PEOPLE
Verse 8 tells us that Isaac grew and was weaned – which means he was now around 2-3 years old. In that culture, this was a big milestone because infant mortality rates were high – so surviving those first few years was something worth celebrating. No wonder Abraham held a feast. You can imagine the laughter, the music, and the aroma of food in the air. But then something unexpected happens – verse 9, “Sarah saw that the son whom Hagar the Egyptian had borne to Abraham was mocking.” Interestingly, the Hebrew word for “mocking” comes from the same root as Isaac’s name – which means “to laugh.” The irony was deliberate in that the one whose name means “laughter” was now being laughed at. Now, Ishmael would’ve been around 16-17 years old by this point – which means he was old enough to understand what was happening. For 13 years, he had been the only son – but now Isaac had stolen the spotlight. And because of Isaac, he was no longer going to be at the center of Abraham’s attention. So, out of jealousy and resentment, he mocked Isaac. This wasn’t playful teasing – it’s as if he was saying, “Really? This little boy is supposed to carry our family? This is the miracle child everyone’s celebrating?” In fact, this is how Paul interprets this scene in Galatians 4:29: “At that time the son born according to the flesh persecuted the son born by the power of the Spirit.” Ishmael was persecuting Isaac. Now, Sarah’s response was harsh – verse 10: “Get rid of that slave woman and her son, for that woman’s son will never share in the inheritance with my son Isaac.” This deeply distressed Abraham because Ishmael was his son, too. In fact, years earlier in Chapter 17, Abraham had even pleaded that Ishmael would be used as the promised child to bless the nations. So, you could understand why he would be frustrated. But to his surprise, God told him to listen to Sarah. Verse 12, “Do not be so distressed about the boy and your slave woman. Listen to whatever Sarah tells you, because it is through Isaac that your offspring will be reckoned. I will make the son of the slave into a nation also, because he is your offspring.” It’s as if He were saying, “Abraham, trust Me. I won’t abandon them. I will take care of them, too.” Now, despite God’s comforting words, this must have torn Abraham’s heart in two. The promise had come, but it would cost him greatly. He couldn’t understand why, but here, God was asking him to trust again – to believe that separation was necessary for His promise to continue. So, the next morning, he sent Hagar and Ishmael away with some food and water. But out in the wilderness, they quickly found themselves out of water. And it’s at that moment she gave up hope because there was nothing she could’ve done to help her child. They were doomed. So, she placed the boy under a bush – implying that Ishmael didn’t even have the strength to stand on his own. And because Hagar couldn’t watch her son die, because she couldn’t even bear to hear her son die, she walked away and wept at a distance. But just as when she thought everything was over, God called out – “Don’t be afraid, Hagar. I heard the cries of your boy. I have not abandoned you. I will make him into a great nation.” That is grace. Even though Hagar and Ishmael were outside the covenant line, they were not outside His compassion. So, He opened her eyes to see a well of water that was there all along – and He renewed His promise to bless Ishmael and make him into a great nation.
There are two things we see here. First, God refines His people by cutting away whatever threatens our trust in Him. If we read this story at face value, we could come away thinking that we could cut away any family member who is troublesome. But that’s obviously not what this is about. Then, why does God allow something so horrible to happen – casting away Hagar and Ishmael? Paul helps us to understand this better in Galatians 4. There, Paul interprets this story as an allegory to communicate an important truth. If I can summarize, Hagar represents human effort (trying to fulfill God’s promise in our own strength), while Sarah represents divine grace (receiving what only God can give). This makes sense, considering that Ishmael was born through Sarah’s scheming while Isaac was born through faith in God’s promise. Then, here’s what Paul wanted us to know: God will prune whatever competes for our faith – not to punish us but to free us. At times, God will ask us to surrender something that isn’t evil in itself but has taken the place that belongs to Him. Maybe it’s your reputation, your success, your relationship, or even your religious performance. And like Abraham, obedience may feel like loss, but pruning is an act of love. God cuts away anything that competes with His grace so that we would never rely on ourselves. Think of it this way: He frees our hands so that we can cling more tightly to Him. Second, God provides for the broken. The same God who chose Isaac still heard Ishmael’s cries – He does not abandon the outcast. Now, if He does that for those outside the covenant, how much more will He care for us – His sons and daughters in Christ? Romans 8:32 says it like this: “He who did not spare His own Son, but gave Him up for us all – how will He not also, along with Him, graciously give us all things?” That’s the heart of our God: faithful to His promise, merciful to the outcast, and near to the brokenhearted. So, friends, no matter the season you may be in, be confident that He’ll take care of you. He’ll refine you not to diminish your joy but to deepen it.
3) GOD EXTENDS HIS BLESSING
If the last story showed Hagar and Ishmael walking away from Abraham, this one begins with someone walking toward him – King Abimelek. We first met him in the previous chapter. He was the man Abraham deceived – the one who unknowingly took Sarah as his wife, only for God to intervene in a dream to stop him from doing something sinful. So, humanly speaking, Abimelek had every reason to resent Abraham. But in verse 22, Abimelek approached Abraham not to accuse him, but to make peace – “God is with you in everything you do. Now swear to me here before God that you will not deal falsely with me or my children or my descendants. Show to me and the country where you now reside as a foreigner the same kindness I have shown to you.” He was basically saying, “There’s something different about you. You’re not the same person I knew. Everything you touch turns into gold. God must be with you – and I think it’s best for me to stick with you.” Something had changed in Abraham. The man who once lied out of fear now lived with integrity. The man who acted deceitfully to protect himself now acted righteously to reflect God. Abraham had been humbled, refined, and shaped by grace – and the long years of waiting and testing have matured his faith so that he was no longer driven by self-preservation but by trust in the Lord. And as a result, he truly became a blessing to the nations just as God promised in Genesis 12. This is clearly seen when Abimelek asked for a covenant. Even when there was a dispute about a well, Abraham didn’t demand or threaten. In fact, he simply offered seven lambs as a symbolic gesture to affirm ownership of the well – which shows that Abraham never took things for granted. He was never entitled. He didn’t use his power to exploit the situation. He paid fairly and acted with transparency and humility. And it resulted in peace, mutual respect, and a public testimony that God’s people live differently. Now, after the covenant, Abraham planted a tamarisk tree – a desert tree that grows slowly but lives long, often symbolizing endurance and stability. So, planting this tree was his way of saying, “The God who has been faithful to me now will continue to remain faithful forever.” And then he worshiped the Lord, not because there wouldn’t be any more troubles in his life, but simply because He had found peace and purpose in the Lord. In verse 34, we see that he was still a sojourner – in that he still had no place to call home. But his faith was anchored in the Eternal God – and that enabled him to worship through it all and be a blessing to those around him.
What does this mean for us? The truth is that all of us are sojourners in this life. This is not our home. It’s a place where God called us to reflect His glory to the nations – but this is still not our final destination. Then, how should we live in this world? By being a blessing to others. What does this mean practically? It means living in such a way that people can see the presence of God in us. It means showing kindness in a world that’s quick to criticize, choosing patience when everyone else is in a hurry, and offering grace when others expect judgment. It means working with integrity when no one is watching and serving others without needing recognition. It means opening your home, your wallet, and even your schedule to love those who can give you nothing in return. It means being a voice of peace in places of conflict, a listener in a culture of noise, and a light in moments of darkness. It means forgiving when it’s costly, giving when it’s inconvenient, and praying even when it feels unseen. It means seeing your neighborhood, classroom, and workplace as your mission field – places where you can reflect the character of Christ. All that to say, to be a blessing is to live as a window through which others can see the goodness and faithfulness of God. Jesus said it this way in Matthew 5:16, “Let your light shine before others, that they may see your good deeds and glorify your Father in heaven.” This is what Abraham learned to do – and this is what we’re called to do. The mark of mature faith is not just believing God’s promises but reflecting His character. Brothers and sisters, this world is watching us – to see if God we say we love truly is real. So, let me ask you: When they look at your life, do they see the faithfulness of the Eternal God? Do they see peace where others would panic? Joy where others would despair? Grace where others would seek revenge? If God has shown you grace, if He has carried you through the waiting and the refining, embody His presence in all that you do, knowing that the God who blessed Abraham to be a blessing has blessed you for the same purpose.
CONCLUSION
Lighthouse family, our God is the God who fulfills His promise, refines His people, and extends His blessing. Then, let’s learn to wait faithfully, obey fully, and live beautifully for His glory so that the world will know that He alone is worthy of our worship.
DISCUSSION QUESTIONS
1) Abraham and Sarah waited 25 years. How might God be using your own season of waiting to deepen your faith or shape your obedience?
2) What are some “Who would have thought…” moments in your life or in our church community that reveal God’s power to make the impossible possible?
3) Why do you think we sometimes protect ourselves from disappointment by lowering our expectations of God? What would it look like to hope again?
4) In what ways has God “cut away” things in your life that were good in themselves but had begun to take His place? How did that process refine your faith?
5) Why do you think Abimelek, a pagan king, could recognize that “God is with you in everything you do”? What might that look like for people to see God’s presence in our lives today? What does it practically mean to “be a blessing” where God has placed you – in your home, neighborhood, or workplace?
