¹⁸ it was he to whom it was said, “In Isaac your descendants shall be called.”

Why Isaac? What about Ishmael? Islam claims that the Jews and Christians have it all wrong, that Ishmael, as the firstborn, was the son of promise, not Isaac. Of course, that would require the charge that the Christian Old Testament (and the Jewish Torah) were corrupted, obscuring what Muslims believe was the real story of Abraham. However, there is no historical or literary evidence substantiating such a charge. Furthermore the primacy of Isaac’s descendants (through Jacob) is so ubiquitous throughout Scripture that any suggested corruption would have to have affected the entire strand of biblical history and literature. This, of course, cannot be sustained.

We affirm that, “God, after He spoke long ago to the fathers in the prophets in many portions and in many ways, in these last days has spoken to us in His Son, whom He appointed heir of all things, through whom also He made the world” (Heb 1:1–2). Both Jesus and the prophets affirm the primacy of God’s promise to Abraham and the descendants of his son, Isaac.

Furthermore, this Jesus who is a descendant of Abraham, Isaac and Jacob, “… is the radiance of [God’s] glory and the exact representation of His nature, and upholds all things by the word of His power. When He had made purification of sins, He sat down at the right hand of the Majesty on high, (Heb 1:3). There was and is no further need of revelation or any further prophet after Jesus. He is God’s complete statement to us today.

But why the specificity of Isaac? After all, Ishmael was also a son of Abraham. Why did it need to be through Sarah? The Scripture does not give us a specific answer, but there some things we do know or can surmise about this. First, the Creator of all the earth does not need to explain all of His actions and commands. The book of Job presents this clearly, the plight of a man who did not understand the reason for his suffering. God does not need to explain Himself.

Second, the Lord may have been affirming the significance of marriage. Ishmael was not his legitimate child through Sarah his wife, but through her servant girl, Hagar. Clearly Abraham’s impregnating Hagar was a scheme concocted in unbelief by Sarah (and his obvious complicity) to circumvent what seemed to be God’s failure in allowing Sarah to become pregnant (Genesis 16:1-4). Human compromises can never replace faith in the Word of God. Abraham and Sarah learned the hard way. God protect us from this same error.

Lord, help me to patiently wait for Your promises in my life and not settle for my humanly devised shortcuts to Your blessings.