(1) God made the covenant with Abraham as the means of dealing with evil within the good creation, which meant dealing in particular with evil within human beings, Gods image-bearers. This I have already explained.
(2) The family of Abraham, who themselves share in the evil, as well as in the imagebearing vocation, of the rest of humanity, treated their vocation to be the light of the world as indicating exclusive privilege. This was their own meta-sin, their own second-order form of idolatry, compounding the basic forms they already shared with the Gentiles. This further point is basic to Pauls critique of Israel in such passages as Romans 2, 7 and 10 and Galatians 2, 3 and 4.
(3) When God fulfils the covenant through the death and resurrection of Jesus and the gift of the Spirit, thereby revealing his faithful covenant justice and his ultimate purpose of new creation, this has the effect both of fulfilling the original covenant purpose (thus dealing with sin and procuring forgiveness) and of enabling Abrahams family to be the worldwide Jew-plus-Gentile people it was always intended to be. Indeed, when we rightly understand the matter, we shall see that from Pauls perspective at least these two effects were so closely aligned with one another that they not only could be spoken of in the same breath but demanded to be thought of as the same thought.
Creation and Covenant by N.T. Wright