The reason why God could give us an allegory of the law so long before the law was delivered on Mount Sinai and even before Moses was born, is because these things were not in fact new. Ishmael and Isaac represented those under the law and those under grace, but these two types of man have existed since the beginning of the world. The law is written on the heart of every man and woman who comes into the world and all are born under the covenant of works because of their relationship with Adam. Grace too has been operating in the world since the time of the first promise given in Genesis 3:15 in which Christ’s victory over the devil was foretold. What the formal giving of the law on Sinai did was to remind the physical descendants of Abraham that their relation to Abraham did not in itself set them free from the law, but only gave them a gateway to salvation. If they followed the example of their forefather and believed in God they would be saved, but if they trusted in their physical descent from Abraham, they remained under the original covenant of works made with Adam.