Question 1: When Abraham believed the promise of God, what was the promise that he believed exactly?
Answer 1: That all the heathen would be converted.
Q 2: If Jesus died in order that the blessing of Abraham might come to the Gentiles, does this mean that God promises Abraham that Christ would come to die as a sacrifice, in order that the promise to Abraham might be fulfilled? Did Abraham understand this?
A 2: Yes, and yes.
Q 3: Why does Paul argue that going back to the old, pre-Messiah order was an impossibility?
A 3: Because the old order was in bondage, and Christ accomplished freedom from all bondage. Christ is the new witness of Himself in the new order.