Calvin writes:
Now, as to the new covenant, it is not so called, because it is contrary to the first covenant; for God is never inconsistent with himself, nor is he unlike himself, he then who once made a covenant with his chosen people, had not changed his purpose, as though he had forgotten his faithfulness. It then follows, that the first covenant was inviolable; besides, he had already made his covenant with Abraham, and the Law was a confirmation of that covenant. As then the Law depended on that covenant which God made with his servant Abraham, it follows that God could never have made a new, that is, a contrary or a different covenant. For whence do we derive our hope of salvation, except from that blessed seed promised to Abraham? Further, why are we called the children of Abraham, except on account of the common bond of faith? Why are the faithful said to be gathered into the bosom of Abraham? Why does Christ say, that some will come from the east and the west, and sit down in the kingdom of heaven with Abraham, Isaac, and Jacob? (Luke 16:22; Matthew 8:11) These things no doubt sufficiently shew that God has never made any other covenant than that which he made formerly with Abraham, and at length confirmed by the hand of Moses. This subject might be more fully handled; but it is enough briefly to shew, that the covenant which God made at first is perpetual.
Urban Reformed Theology 