How was Isaac Abraham’s only son?

Difficult Passages · Who, Where, and Which

How was Isaac Abraham’s only son?

Isaac was the only son of Sarah, the only son of the promise, and the only son left in Abraham’s house.

The Passages

Genesis 22:2

2 And he said, Take now thy son, thine only son Isaac, whom thou lovest, and get thee into the land of Moriah; and offer him there for a burnt offering upon one of the mountains which I will tell thee of.

Genesis 16:15

15 And Hagar bare Abram a son: and Abram called his son's name, which Hagar bare, Ishmael.

10 Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, even with Isaac. 11 And the thing was very grievous in Abraham's sight because of his son. 12 And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called. 13 And also of the son of the bondwoman will I make a nation, because he is thy seed. 14 And Abraham rose up early in the morning, and took bread, and a bottle of water, and gave it unto Hagar, putting it on her shoulder, and the child, and sent her away: and she departed, and wandered in the wilderness of Beersheba.

The Difficulty

God said to Abraham, “Take now thy son, thine only son Isaac, whom thou lovest” (Genesis 22:2), and Hebrews calls Isaac his “only begotten son” (Hebrews 11:17). But “Hagar bare Abram a son: and Abram called his son’s name, which Hagar bare, Ishmael” (Genesis 16:15).

The Answer

Isaac was Abraham’s only son by Sarah his wife; Ishmael was the son of the bondwoman. He was the only son of the promise: God had said, “in Isaac shall thy seed be called” (Genesis 21:12), and Hebrews joins the two at once, “his only begotten son, Of whom it was said, That in Isaac shall thy seed be called” (Hebrews 11:17–18). And he was the only son then in Abraham’s house: at God’s word Abraham had sent Ishmael away with his mother (Genesis 21:12–14). Gill gives these. “Only son” names Isaac as the son God had given and now asked for, the one in whom all the promises stood.

Sources

John Gill, An Exposition of the Old Testament, vol. 1 (1763), p. 139, on Genesis 22:2

for, though Ishmael was his son, he was a son by his maid, by his concubine, and not by his wife; Isaac was his only legitimate son, his only son by his lawful wife Sarah; the only son of the promise, his only son, in whom his seed was to be called

Checked against: Internet Archive scan of the first edition, 2026-10-28