God makes a covenant with Abram. Makes him fertile and promises his offspring the land from the Nile to the Euphrates… the “Promised Land” after 400 years in captivity.
The Patriarchs and the Prophecies make up a majority of the Pentateuch, AKA, the Torah.
The primeval history sets out the author’s (or authors’) concepts of the nature of the deity and of humankind’s relationship with its maker: God creates a world which is good and fit for mankind, but when man corrupts it with sin God decides to destroy his creation, saving only the righteous Noah to reestablish the relationship between man and God.
The Ancestral history (chapters 12–50) tells of the prehistory of Israel, God’s chosen people. At God’s command Noah’s descendant Abraham journeys from his home into the God-given land of Canaan, where he dwells as a sojourner, as does his son Isaac and his grandson Jacob. Jacob’s name is changed to Israel, and through the agency of his son Joseph, the children of Israel descend into Egypt, 70 people in all with their households, and God promises them a future of greatness. Genesis ends with Israel in Egypt, ready for the coming of Moses and the Exodus. The narrative is punctuated by a series of covenants with God, successively narrowing in scope from all mankind (the covenant with Noah) to a special relationship with one people alone (Abraham and his descendants through Isaac and Jacob).
I think more important to the story is prophesy of the 400 years of captivity:
And he said unto Abram, Know of a surety that thy seed shall be a stranger in a land that is not their and shal server them; and they shall afflict them four hundred years;
And also that nation, whom they shall server, will I judge: and afterward shall they come our with great sustenance.
And thou shalt go to thy fathers in peace