In Genesis 21, Abraham’s household reached a breaking point. Two sons were living under one roof: Ishmael, born of Hagar, and Isaac, born of Sarah by God’s promise. Sarah finally said, “Cast out this slave woman with her son, for the son of this slave woman shall not be heir with my son Isaac” (Genesis 21:10).
At first, Abraham resisted. It was painful to let one go. But God confirmed Sarah’s words: Isaac—the child of promise—would be the heir.
This story isn’t just about family tensions thousands of years ago. Paul tells us in Galatians 4 that it’s a picture of something far deeper. Hagar represents the law. Sarah represents the promise. Ishmael was born through human effort, but Isaac was born through God’s power. And the truth is clear: law and grace cannot live together in the same household.
The law has its purpose. It reveals our sin and shows us our desperate need for God. But when we live under it, the voice of the law sounds like demand and condemnation:
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“Do better.”
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“You’re still not enough.”
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“If you don’t get this right, you’re out.”
It drives us to work harder, but never brings peace. Grace speaks a different word. It doesn’t deny sin, but it points us to Christ who has already fulfilled the law. Grace whispers:
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“It is finished.”
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“You are Mine.”
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“Rest in what I’ve done.”
The law says, “Do to live.” Grace says, “It is done—now live.”
One voice heaps on fear. The other gives freedom. If you’ve ever wrestled with thoughts like, “I’ll never measure up” or “Maybe God is done with me,” pause and ask: Whose voice am I hearing?
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The voice of law condemns and leaves you hopeless.
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The voice of grace convicts but always leads you back to Jesus.
God’s voice never drives His children into despair—it draws them into His arms.
Just as Abraham’s household couldn’t hold both Ishmael and Isaac, your heart cannot cling to both law and grace. Only one can be the heir.
Choose grace. Rest in Christ. Let His voice be the one that shapes your steps and steadies your soul.
A Prayer
Lord, thank You that I am not a child of slavery, but of promise. Help me silence the condemning voice of the law and hear the gentle voice of Your grace. Teach me to live as Your beloved, free in Christ. Amen.
