Expositor's Bible Commentary Commentary Galatians 4:23

"Howbeit the [son] by the handmaid is born after the flesh; but the [son] by the freewoman [is born] through promise." — Galatians 4:23 (ASV)

There were two main differences between these sons. (1) They were born of different mothers (v.22); one was a free woman, the other a slave. This, according to ancient law, also affected the sons’ status. (2) In the manner of their conception, Ishmael’s was entirely by natural means (Abraham was elderly at the time, but still the conception was natural), whereas Isaac’s was by means of a miracle (by this time Abraham had passed the age at which it was normally possible to engender children and Sarah was long past the age of conceiving them). Isaac was brought into being “as a result of a promise” from God.

This contrast lends itself well to the distinction Paul is trying to make between natural or man-made religion and supernatural or God-made religion. The religion of works and law corresponds to the natural birth of Ishmael; the religion of the Spirit, which is Christianity, corresponds to the supernatural birth of Isaac.