The name of Abraham is repeatedly invoked throughout the Old Testament, especially on those occasions when God acts according to His covenant promises in order to bring salvation to the nation of Israel (Ex. 2:23–25; 2 Kings 13:22–23). Indeed, the old covenant prophets could appeal to the mighty work the Lord did with Abraham to give the Israelites hope in their darkest hours.
Such invocation of the memory of Abraham is precisely what Isaiah does in chapter 51 of his book. Isaiah’s prophecy is addressed first to those Israelites who would suffer exile in Babylon. Due to the nation’s infidelity and the proclivity of the Davidic king to trust in foreign alliances instead of Yahweh, the one, true Lord of all, God pledged to expel the southern kingdom of Judah from its homeland and send it off to Babylon (chap. 39). Exile would not be the last word for the Israelites, however, for Isaiah also prophesied that God would return a remnant to the land, execute His covenantal curses for disobedience on a Davidic representative of the nation, and bring in a new heavens and earth (chap. 40–66).
Because few Israelites would leave their homes in exile for the land of Judah, which the Babylonians had pillaged and all but destroyed centuries earlier, the Lord knew that the remnant returning from exile would be discouraged at times. So in Isaiah 51, He called Israel to remember father Abraham and mother Sarah. Just as they were few in number and faced impossible odds in bearing a son, so too would the remnant be small and powerless, humanly speaking. Yet just as He brought forth descendants from a couple “as good as dead” (Heb. 11:12), so too would God accomplish the impossible in the remnant. If this remnant in Judah trusted the Lord, they would be restored and their restoration would bring blessing to the whole world. The peoples and the nations would see God’s righteousness and justice and be blessed (Isa. 51:5), just as God promised Abraham centuries earlier (Gen. 12:1–3).
Many of the returned exiles lacked faith, so the restoration was not initially as glorious as it could have been. But a righteous remnant continued to trust the Lord, and the faith of this remnant was vindicated when God sent His Son, who is also the Son of David, to inaugurate the Abrahamic blessing (Luke 1:67–80).