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The Birth of Isaac

by Stephen Davey Scripture Reference: Genesis 20–21

It’s comforting to know that through all our failures and faithlessness, God never changes. His promises will never be broken. The birth of Isaac is proof of that. God’s work is not dependent on any of us, but He graciously allows us to be a part of His plan, as we follow Him.


Did you know that GPS systems have to be recalibrated every decade or so? That’s because the earth’s crust is actually moving, and without GPS recalibration, you wouldn’t make it to the right address, and your packages would be delivered to your neighbor’s house.


That reminds me that we need to periodically recalibrate our lives according to God’s unchanging Word. Although the world around us is shifting and changing, God’s promises never do.


Sometimes it seems like people are trying to keep God’s promises from coming true. Here in Genesis 20, Abraham’s lack of faith looks like it’s going to derail God’s promise of a son through his wife Sarah (17:15-21). Abraham and Sarah have been waiting on that promise for decades.


Verse 1 says, “Abraham journeyed toward the territory of the Negeb and lived between Kadesh and Shur; and he sojourned in Gerar.” 


Once again, in verse 2 Abraham tells the lie that Sarah is his sister in order to save his skin from the Philistine king, Abimelech. He’s afraid the king will kill him to get his beautiful wife. Abraham pulled the same stunt earlier, in Egypt, for the same reason.


Maybe the first time Abraham did this back in Egypt was understandable. He was fairly new to walking by faith. But he knows better now—some twenty-five years later. God has spoken directly to him many times since then, promising him that Sarah will have that promised son; and from that son will come a nation, and from that nation will come the Savior who will redeem mankind.


In one sense Sarah is Abraham’s sister. In verse 12 Abraham reveals that Sarah is his half-sister—they have the same father but different mothers. And as we’ve already explained, before the law of Moses was given, such marriages weren’t forbidden as they are today—in order to protect us from a myriad of physical problems that now occur in the offspring when close family members marry.


But Abraham is hiding behind this half-truth. The real truth is, he’s afraid. He’s not so confident that God’s word is unchangeable.


Maybe you can point to times in your life when your faith was strong in God’s promises, but also to other times when you’ve felt weak and faithless. Well, let me encourage you here that God’s promises to Abraham aren’t dependent on how strong Abraham is but on how strong God is. Even our failures can’t derail God’s promises.


Genesis 20:2 tells us, “Abimelech king of Gerar sent and took Sarah.” He’s going to add her to his harem after all. But to his credit, he doesn’t know she’s married to Abraham.


But in verse 3, God comes to Abimelech in a dream and says, “You are a dead man because of the woman whom you have taken, for she is [another] man’s wife.”


Verse 4 tells us that he hadn’t touched her yet, and God says to him in verse 6, “It was I who kept you from sinning against me. Therefore I did not let you touch her.” God tells Abimelech in his dream to give Sarah back to Abraham. 


The king does so, and Abraham then acts in the role of a prophet of God and prays for Abimelech in verse 17. God is guarding Abraham and Sarah from any retaliation from this king.


Isn’t it wonderful that the promises of God don’t depend on your faithfulness but on His? Yes, your own sin and selfishness have consequences you might have to live with, but God isn’t up in heaven wringing His hands, hoping you don’t mess up His plans. My friend, even your sin isn’t greater than God’s power and mercy and grace. 


Let me show you that God’s promises can’t be stopped by Sarah’s jealousy. 


Genesis 21 begins in the delivery room when God’s promise is fulfilled and ninety-year-old Sarah delivers a baby boy. A one-hundred-year-old Abraham is out there in the waiting room dancing around with joy. They finally have their promised son, and Abraham names him Isaac.


Ishmael is around fifteen years old at the time. You remember, he’s the offspring of Abraham and Hagar, Sarah’s handmaiden whom Sarah had arranged in unbelief to bear a child for Abraham. Frankly, you can sympathize with Ishmael here; he’s no longer the heir to Abraham’s fortune. He’s not part of the covenant promise of the Hebrew nation. And his resentment and unbelief is beginning to show.


We’re told in verse 9 that Sarah sees him mocking Isaac. She is understandably upset, but then she demands that Abraham exile Hagar and Ishmael once and for all.


Abraham is torn by Sarah’s sinful attitude toward his oldest son. But the Lord comes along and says to Abraham:


“Whatever Sarah says to you, do as she tells you, for through Isaac shall your offspring be named. And I will make a nation of the son of [Hagar]also, because he is your offspring.” (verses 12-13)


Notice how gracious the Lord is with Ishmael. He’s Abraham’s son too, and he will be blessed to father a nation. Even though Isaac is the heir of the covenant promise, God has a plan for both Isaac and Ishmael.


It’s easy to overlook the fact that neither of these boys had any say in the circumstances they were born into. But they did have a say in how they would respond to God; we’ll learn that Ishmael will reject the God of Abraham, and Isaac will choose to follow Him.


Abraham sends Hagar and Ishmael away into the wilderness with the Lord’s promise of taking care of them. But it isn’t long before Hagar runs out of water in the wilderness of Beersheba, and she begins to weep. Frankly, it’s a touching scene of despair. 


God arrives in verse 19 and miraculously opens Hagar’s eyes, and she sees a “well of water.” She and her son are saved from certain death. 


Chapter 21 goes on to tell us that Ishmael grew up and married a woman from Egypt, beginning a family that would eventually become the Arab nation. God’s promises to him came true as well.


I can’t help but feel for Hagar and Ishmael here. The wilderness can be a terribly lonely place. Maybe you’re suffering right now in your own version of the “wilderness” and you’re wondering about God’s promises of caring for you and guiding you. The winds of doubt have blown the sands of despair in your eyes, and you can’t see the way forward. 


This is the best place to be reminded of the promises of God. Mistreatment, hopelessness, sinful people, or your own sinful failures cannot prevent the promises of God from being fulfilled.


At this point in Genesis 21, King Abimelech comes to Abraham and negotiates a peace treaty between his nation and Abraham. The peace treaty is ratified by Abimelech, giving Abraham a well, and Abraham gives Abimelech seven lambs as a “witness,” or proof, of Abraham’s ownership of the well.


Don’t miss this significant moment: Abraham now owns a well and a plot of land. This is the first piece of real estate he owns in the promised land—a land God was promising to Abraham and his descendants as an eternal inheritance. 


Abraham plants a tree by this well and holds a worship service in honor of the Everlasting God.


And with that, Abraham is moving forward again in faith. You and I can do the same, not because we’re without sin or because we’re always faithful. We move forward by trusting the Word of God, which will not change—even though the very crust of the earth can’t stop moving and shifting. We can trust in the Rock of Ages and His unchanging, faithful Word.

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