Genesis 22:16-18 records God's embellishment of the promise on the occasion of Abraham's "sacrifice" of his son Isaac. God promises to multiply Abraham and to give him control of strategic military and commercial positions, "gates," in his enemies' territories. As we will see, this promise speaks of the geopolitical advantage God later gave Abraham's descendents. God bases this promise on Abraham's obedience of the command to sacrifice his son, Isaac, a sacrifice God of course stopped just before the knife fell. Note, too, that this promise has the effect of an oath, in that God swears by Himself.
Since this is the last recorded promise to Abraham, it is fitting that God should refer to His first promise, recorded in Genesis 12:1-3. God reminds Abraham of His promise that his seed would be a blessing to all nations. In Galatians 3:16, Paul makes it plain that this "Seed" is Christ. Christ, who is in the lineage of Abraham, blazed a trail by which all peoples could ultimately develop a relationship with the Father. Christ's work makes it possible for God to be our God, according to the promise of Genesis 17:7-8. Christ is indeed a blessing to all nations.
Searching for Israel (Part One): The Promises to the Faithful