More details of this key covenant in the Old Testament can be found in Genesis 12:2-3, which goes into the promise that God makes Abraham and how he plans to use Abraham to bring about his purposes and achieve his will:
I will make you into a great nation,
and I will bless you;
I will make your name great,
and you will be a blessing.
I will bless those who bless you,
and whoever curses you I will curse;
and all peoples on earth
will be blessed through you.
God's covenant with Abraham concerns the way that God has chosen Abraham to be, literally, as the name indicates, "father of a multitude." God has selected Abraham to be the father of his people, God's chosen people, that are meant to show the rest of the world what a relationship with God looks like. This is why God promises to make Abraham's descendants a mighty nation and to give them his special blessing. In this chapter we also see the land that God promises to give to Abraham's descendants as God's promised land to them.