Some portions of Scripture are more oblique than others—this section on Hagar and Sarah is one of them. As already mentioned, Paul employs allegory to illustrate his point; he used the OT story of Abraham’s offspring from two different women (one a servant girl, the other his wife).

The question naturally arises that if the new covenant of grace is in fact traced back to Abraham, then how does one explain the delay in its manifestation among God’s people? Why had the Law been in force all that time, from Moses to Jesus? Although Paul doesn’t give an answer to that question directly, he does find an analogy in Isaiah. Israel struggled with the same issue during the prophets’ time. Paul quotes the verse that immediately follows Isaiah 53, the so-called Suffering Servant song, depicting Christ’s death. The Jews tend to see that chapter as depicting the sufferings of the people of Israel; they are the “suffering servant.” The point is that long suffering is intrinsic to Israel’s existence, waiting on God’s promises. Paul likens the wait for grace to Isaiah’s depiction of a barren woman who waits long for a child. The coming of the message of grace through Jesus Christ is like such a woman who finally gives birth.

Gentile believers (since that is who Paul is writing to) have now, through faith, come into the standing of sons of the promise. Isaac was the son of Sarah, he was the one through whom the promise of blessing was to pass. Though the promised passed down the genealogical line through Isaac, Jacob and the descendants of the twelve sons of Jacob, now the line of inheritance is passed on to and through those who have faith in the Lord Jesus Christ. The choice then is whether to forever associate with the Law of Moses or to embrace the coming of the blessing promised beforehand to Abraham.

The quotation from Isaiah also points out that the children in question, those of the new, heavenly Jerusalem, will be more numerous than those of the old, early Jerusalem. In fact, they will include both believing Jews and believing Gentiles. All those who believe are raised up in status, not to the position of being fellow children under the Law which brings slavery to the Law, but to the higher position, fellow children of promise, citizens of the new, heavenly Jerusalem, which brings freedom in Christ. Praise God.