Part of the promise given to Abraham and Sarah included the promise of a son who would be their heir. A baby born to a couple who were 100 years old and 90 years old – Wow! Promise fulfilled. Baby born. Prayer answered.
The promise went beyond this couple, though. Miraculous though it was, it pointed forward to a more miraculous birth. The birth of Isaac was indeed incredible. Even though people lived longer in those days, it was still amazing that this old couple had their first child at their age.
Jesus’ birth was even more amazing. It was amazing because the Holy Spirit conceived the baby, yes (Matt. 1:18). Jesus’ birth was even more amazing than the birth of Isaac. Isaac was promised, but Jesus is The Promised One. The entirety of the Old Testament points forward to the birth of the Promised One. The story of the birth of Isaac is just one point in the strand of God’s promise of salvation from the Old Testament.