Salvation Through the Ages, Chap. 5, The Age of Promise
From Abraham to Israel
People who can't communicate can't work or live together, so after Babel people were forced to carry out God's command to spread out over all the earth. This resulted in the specialization of ethnic groups globally. God then chose one man, Abram (later to be called Abraham), to establish a unique people group that would eventually produce the promised Savior.
Recalling our earlier look at the problem of the purity of the human genome, we can see more significance in the need for a certain genetic line to accomplish what God promised. This is the first explicit step in fulfillment of that promise since it was made.
Yet we still are not given a lot of official divine instruction about salvation in this age. Abraham simply believed what God promised him, and this was all it took to have him declared righteous. He certainly had his faults, but he was no rebel against God. Neither do we get the sense that Abraham was a gambler who decided to take a chance on God, but rather that he trusted God because he knew him. This reminds us of Enoch who "walked with God".
This is a relationship built upon trust, and in that respect it is very much like salvation today. So as with the previous age, salvation was no more specific or detailed than trusting God and his promises, and living in peace with other people. Yet this still predates the giving of the Mosaic law by 430 years. And since the line of promise was through Isaac and Jacob but not Ishmael, not all who descend from Abraham physically or spiritually are Israel. What Paul said about "spiritual Israel" was said about Jews who accepted their Messiah, not Gentiles who did so. Otherwise the church would need to accept Israel's curses along with its blessings, which those teaching they are the same entity never seems to do.