Passage: Genesis 21:1-13

The Big Idea

God likes promises, and He always keeps them. At the set time, just as He said, Sarah had a son, and laughter filled the tent. Abraham could have enjoyed the rest of that promise for twenty-five years before it arrived. Then God told Abraham to send away Ishmael, the child of the flesh, because flesh and Spirit can’t share the inheritance. Every one of God’s promises is “yes” in Jesus, and the Spirit is our guarantee.

God Likes Promises

One Bible teacher counted some 8,800 promises in Scripture, the vast majority in the Old Testament, with Deuteronomy 28 holding more than any other chapter.

God likes promises! If He owned a football team, they’d be called the Promise Keepers. And their motto would be: If God said it, God will do it!

A promise from God is as good as gold. It’s as sure as reality itself, surer than anything we think is certain, like the sun rising. There’s a better chance of the sun collapsing tomorrow morning than of one of His promises failing.

Here are some of God’s promises we should all know:

God promised to bless Abraham, and through his descendants, the whole world (Genesis 12:2-3).
God promised Israel to be their God and make them His people (Exodus 6:7).
God promised that if we seek Him, we’ll find Him (Jeremiah 29:13).
God promised His steadfast love will never fail (Lamentations 3:22).
God promised blessing to all who delight in His Word (Psalm 1:1-3).
God promised salvation to all who believe in His Son (John 3:16).
God promised that all things work together for good for His children (Romans 8:28).
God promised comfort in our trials; the deeper the hurt, the deeper the comfort (2 Corinthians 1:3-5).
God promised to finish the work He began in us (Philippians 1:6).
God promised peace when we pray (Philippians 4:6-7).
God promised to supply our needs (Philippians 4:19).
Jesus promised abundant life and rest to those who follow Him (John 10:10; Matthew 11:28).
Jesus promised His disciples power from on high (Acts 1:8).
Jesus promised He will come back for us (John 14:3).
God promised new life in Christ now (2 Corinthians 5:17).

When God makes a promise, it becomes part of who He is, part of His character. Even people understand how this works.

In Up From Slavery, Booker T. Washington told of meeting a formerly enslaved man from Virginia. Years before the Emancipation Proclamation, this man had made an agreement with his master to buy his own freedom by paying a certain amount each year, and was allowed to work wherever he wanted while he paid. He found better wages in Ohio and went there. When emancipation came, he still owed his former master about three hundred dollars. Even though the Proclamation freed him from any obligation, he walked most of the way back to Virginia and placed the last dollar, with interest, in his former master’s hands. He told Washington he knew he didn’t have to pay, but he had given his word, and he had never broken his word. He felt he couldn’t enjoy his freedom until he had kept his promise.

No one respects someone who breaks a promise. But when God makes a promise, He keeps it. If God said it, God will do it!

At the Set Time (Genesis 21:1-2)

The LORD visited Sarah as He had said, and did for Sarah as He had spoken. Sarah conceived and bore Abraham a son in his old age, at the set time God had told him.

“At the set time.” The promise was fulfilled right on schedule.

Abraham didn’t get to pick the time.
But he could have lived as if the promise were already reality!

Look back at the past twenty-five years. Every time Abraham believed this promise, he was blessed. He behaved differently. He honored God. And every time he didn’t believe it, he was weak and prone to sin.

Every time! Always the same! Believing a promise of God is called faith.

So even though the fulfillment came at the set time, Abraham had access to the blessings of the promise from the moment it was made. Because God had said it. And if God said it, God will do it!

Even if it’s crazy. Sarah had a son in Abraham’s old age. Physically impossible. Against science. Against common sense. Against everything “cool.”

Isaac (Genesis 21:3-7)

Abraham named his son Isaac, and circumcised him on the eighth day, as God had commanded. Abraham was a hundred years old. Sarah said, “God has made me laugh, and everyone who hears will laugh with me. Who would have told Abraham that Sarah would nurse children? Yet I’ve borne him a son in his old age!”

Already Abraham was investing in his son spiritually, leading the way in righteousness, obeying God in faith.
Sarah was overjoyed at God’s fulfilled promise. She knew how crazy it was that God would do this for her.
She was so happy and at rest.

I just wish they could have lived in that rest for the twenty-five years since the promise was made!

Hebrews 4 says we can enter God’s rest right now. His promises reach us today. We can live as if we already have all the blessings and favor of God, because we do! And the set time when we see them will come.

The Son of the Flesh (Genesis 21:8-13)

Isaac grew and was weaned, and Abraham threw a great feast. But Sarah saw Hagar’s son, Ishmael, mocking. So she told Abraham, “Drive out this slave woman and her son! The son of this slave woman will not share the inheritance with my son Isaac.” This greatly troubled Abraham, because Ishmael was his son. But God told him, “Don’t be troubled about the boy and your servant. Listen to whatever Sarah tells you, for through Isaac your offspring will be named. But I will also make a nation of the slave woman’s son, because he is your offspring.”

“Oh, right, I forgot I have this other kid I really love too: the child of my fleshly efforts, my sin, my best ideas. Maybe he can still be part of my life and God’s plan?”

Why did God tell Abraham to send Ishmael away?

Paul explains that not all of Abraham’s physical descendants are his true children. Rather, “through Isaac your offspring will be named.” That means it isn’t the children of the flesh who are God’s children, but the children of the promise who are counted as offspring. For this was the word of promise: “At this time I will come, and Sarah will have a son” (Romans 9:7-9).

Ishmael and Isaac had the same father, but not the same origin.
One was born of the flesh; the other was born of the Spirit, through promise.
And they lived differently.

It matters where your life comes from. If you only have the flesh to draw on for power, strength and resources, you’ll live like someone with none of God’s Spirit.

Ishmael was born of the flesh. He had only what nature gave him.

Isaac was born of the Spirit and promise, created by a miracle. His life pictures what Paul says: because of God, we are in Christ Jesus, who became for us wisdom from God, righteousness, sanctification and redemption (1 Corinthians 1:30). God produces those things in a life through faith. If God said it, God will do it!

The natural person, living by the flesh, will have none of these, because they only come from Jesus.

“You mean every other religion in the world is wrong?” At this point, yes. Because only Jesus actually supplies the spiritual life we need, and gives it as a gift called grace. If by one man’s offense many died, how much more did the grace of God, and the gift by the grace of the one Man Jesus Christ, overflow to many (Romans 5:15)! The wages of sin is death, but the gift of God is eternal life in Christ Jesus our Lord (Romans 6:23).

Isaac was a child of God, a work of God from beginning to end. It started with a promise and ended with life. A truly spiritual life.

And watch the difference between these two men as their stories unfold:

Isaac liked to meditate, spending time in quiet communion with God (Genesis 24:63). Ishmael tended to fight with everyone around him (Genesis 16:12).
Isaac shared his father’s faith. Ishmael carried more of his father’s worldly side.
Isaac married the bride his father sought for him (Genesis 24). Ishmael married a woman from Egypt, a picture of the world (Genesis 21:21).
Isaac would surrender himself to the point of death to honor God (Genesis 22). Self-sacrifice doesn’t show up in Ishmael’s story.

An unbeliever may display many outward signs of the Christian life: singing, praying, quoting Scripture, following rules. But only a true Christian has a deep, real, intimate relationship with the living God.

The child of the flesh needs to be seen doing good things. The child of promise is content knowing God is with him, and that God has done good things for him.

Paul tells this very story in Galatians: Abraham had two sons, one by a slave woman and one by a free woman. The son of the slave was born according to the flesh, and the son of the free woman through promise. These things are symbolic of two covenants; one is from Mount Sinai, bearing children for slavery (Galatians 4:22-24). And what does Scripture say? Cast out the slave woman and her son, for the son of the slave woman will not inherit with the son of the free woman (Galatians 4:30).

So why did God tell Abraham to send Ishmael away? Because we can’t live by the flesh and the Spirit at the same time! One of them has to go.

If we push out the Spirit, the flesh takes over.
If we push out the flesh, the Spirit is free to reign, to lead our actions and our hearts.
We must renounce all dependence on the flesh, and refuse to surrender to its desires.

Your Ishmael and Your Isaac

These things were written for us, because each of us has an Ishmael and an Isaac inside.

Our Ishmael is all our natural hopes, dreams, ambitions and desires.
Our Isaac is bound up in God’s promises: the part of us God has given birth to that says, “I will believe. I will trust God’s promises.”

So here’s what Isaac says. I believe:

If I seek Him, I’ll find Him.
His love for me will never fail.
There’s blessing for me as I delight in His Word.
There’s salvation for me because I believe in His Son.
All things will work together for good for me as His child.
I have comfort in my trials; the deeper I hurt, the deeper my comfort.
God will finish the work He started in me.
I have peace when I pray.
God will supply my needs.
Jesus gives me abundant life and rest as I follow Him.
I receive power from on high as I wait on Him.
He will come back for me.
I have new life in Christ now!

If God said it, God will do it!

“How can you believe so wildly and recklessly? How can you say these things when from the outside they don’t always look true? Isn’t that naive? You sound like a pie-in-the-sky preacher!”

Here’s how: I surrender my doubts to Jesus Christ. I hold my doubts in one hand and Jesus in the other, and when He asks me to believe, I let go of the doubts.

All the promises of God find their “Yes” in Him, and through Him we say “Amen” to the glory of God (2 Corinthians 1:20).

What guarantees every one of these promises? Jesus. All of them are guaranteed!

“Is this promise for me?” Yes!
“Can I rely on these wonderful promises?” Yes!
“Can I depend on them more than my own abilities?” Yes!
“Can I go from being an Ishmael to an Isaac?” Yes!

How? By trying harder? No! By being born of the Spirit.

And how does that guarantee get applied to my own life? God has sealed us and given us His Spirit in our hearts as a guarantee (2 Corinthians 1:22).

Jesus is the guarantee, and the Spirit is Jesus’ very heart and life applied and given to you!

He gives His Spirit to anyone who asks. We need to ask afresh for the Holy Spirit every day, and He’s bound to respond to everyone who asks. It’s His promise! He won’t promise to pay your college tuition when you’re in kindergarten, and then flake out when you graduate and really need Him.

Jesus said to ask, and it will be given; seek, and you’ll find; knock, and the door will be opened. If a son asks his father for bread, will he give him a stone? If you, though you’re evil, know how to give good gifts to your children, how much more will your heavenly Father give the Holy Spirit to those who ask Him (Luke 11:9-13)!

If God said it, God will do it!

Will you believe it? Or will you keep trying your best, rejecting His all-sufficient help and grace in favor of the “I don’t need anything from anybody” idol of self-sufficiency?

Husbands, stop just trying. Start believing His Word, and love your wives as He equips you to.
Wives, stop just trying to please your man, and start believing God’s Word that He sees your heart and is honored by it.

Abraham would inherit the land and become a great nation, because he believed God’s promises. Isaac was just the first of many fulfillments, a miracle of God’s love and faithfulness, not only to Abraham, but to every one of us.

Grace Takeaway

Every promise God makes is part of His character, and at the set time He keeps it. You don’t have to wait for the fulfillment to enjoy the rest of believing it. Send away the Ishmael of your own effort, and let the Isaac of faith inherit. Ask for the Spirit, God’s guarantee, every day. If God said it, God will do it.

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If God Said It, God Will Do It