It's interesting to notice something here—and that is God's foresight. And, I might add here, also His plan. Remember that Abraham didn't have a child yet. But already God is planning a discipline that He is going to put the descendants of Abraham [through], in which they would be subject to others. But also planned was their release from that subjugation, the destruction of the Amorites under Joshua, and the inheritance of the Land. What God is showing is that the events of the exodus were part of a much larger plan, which God inaugurated through Abraham and then continued through Isaac, Jacob, Joseph and Moses. So let's go to chapter 17, where the real covenant was made with Abram.
This is what Paul is explaining here. In all of mankind that has lived since Adam, since the promises were made to Abraham, only one person has qualified to receive the inheritance of the promises that were made to Abraham. That one person was Christ.
You can see the requirements as early as Genesis 17:1, where God said to Abraham, "Walk before Me, and be perfect." Some Bibles translate it, "Be blameless," which means the same thing; "Be without sin." Christ, at the end of His life, was found to be blameless; therefore, He qualified to receive the promises. He met every condition of the Covenant, and then became the inheritor.
