John Sailhamer writes:
1) The author of the Pentateuch wants to draw a connecting link between God's original plan of blessing for mankind [Genesis 1-2] and his establishment of the covenant with Israel at Sinai [Exodus 19]. Put simply, the author sees the covenant at Sinai as God's plan to restore his blessing to mankind through the descendants of Abraham (Gen 12:1-3; Exod 2:24).
2) The author of the Pentateuch wants to show that the Covenant at Sinai failed to restore God's blessing to mankind because Israel failed to trust God and obey his will.
3) The author of the Pentateuch wants to show that God's promise to restore the blessing would ultimately succeed because God himself would one day give to Israel a heart to trust and obey God (Deut. 30:1-10).
From a good article by Sailhamer in Trinity Journal: "Exegetical Notes: Genesis 1:1-2:4a"