This is the beginning of the promise we just read of there in Deuteronomy 1:8, but that promise is gradually expanded to include more.
Instead of just being a vague promise of land, now we have some dimensions that are set, and those dimensions go all the way from the River Nile to the River Euphrates. I am not going to go through the whole promise as it has expanded from time to time, but we are going to jump all the way to Romans 4 and update this into New Testament, New Covenant times.
The promises expanded out of the land of Palestine from between the two great rivers, the River Nile and the River Euphrates, and now we find Abraham is going to inherit the entire world. It gets even greater than that because we find in the book of Hebrews: