The Relationship between the Abrahamic and Mosaic Covenants
The covenant with Abraham was, as we have seen, the source from which the people of Israel were created. But a people without a land can never truly be a nation, and Yahweh had promised that very thing (Gen. 12:2; 17:20; 21:18; 46:3; 48:4. cf. Deut. 7:6-8). A nation’s identity is tied to its surroundings; the familiar topography which is recalled in its literature, poetry and songs (e.g. Psa. 137:1-6). So God promised a specific territory to the physical descendants of Abraham, Isaac and Jacob for an everlasting possession (e.g. Exod. 32:13). In fact, the last mention of Abraham in Genesis is in tandem with Isaac and Jacob and the land (Gen. 50:24). There was an oath-based guarantee of Israel-in-the-land in existence hundreds of years before Moses brought the people to Sinai.
The first chapters of the Book of Exodus are full of allusions to the Abrahamic covenant. Before He had even brought them out of Egypt Yahweh declared He would do so because of this covenant:
So God heard their groaning, and God remembered His covenant with Abraham, with Isaac, and with Jacob. – Exodus 2:24
When God introduces Himself to Moses it is in the context of covenant remembrance (Exod. 6:1-8). The land is once more prominent:
And I will bring you into the land which I swore to give to Abraham, Isaac, and Jacob; and I will give it to you as a heritage: I am the LORD. (Exod. 6:8).
As the Mosaic covenant will be made with the people of Israel prior to them taking possession of the land (although there was a delay through unbelief – Num. 32:11), this indicates that that bilateral covenant was built upon the oath contained in the previous unilateral Abrahamic oath. It follows from this that if the provisions of the Mosaic Law were violated (cf. also Deut. 27 – 30) – which was sure to be the case – the Divine oath uttered to the Patriarchs would be unaffected apart from the time of its fulfillment.
Conversely, if it is assumed that the Sinaitic requirements overrode the promises to Abraham, Isaac and Jacob, then the Mosaic covenant would be the ideal way to frustrate the revealed plan of God up to this point in the biblical narrative. The Creation Project would have had to be rerouted so as to bypass human depravity and dereliction. But that was not the case. Moses knew that he could appeal to God’s covenant with Abraham and so ensure the survival of the disobedient nation. When God threatened to destroy the people after the episode concerning the golden calf, Moses successfully interceded for them by claiming the Abrahamic pledges.
Remember Abraham, Isaac, and Israel, Your servants, to whom You swore by Your own self, and said to them, ‘I will multiply your descendants as the stars of heaven; and all this land that I have spoken of I give to your descendants, and they shall inherit it forever. – Exodus 32:13
Moses is careful to include both of the main strands of the Abrahamic covenant, that is, land and seed (descendants), which concern Israel as a new nation created by God. And we will see that this pattern repeated continually; one might say habitually, by the writing Prophets.
Even though Israel is spared through the intercession of Moses, and delivered through the waters of the Red Sea, there is no final salvation through the Mosaic covenant (cf. Rom. 3:19-20; 4:15). The covenantal nature of the Law, though it does not rule out an approach to God through sacrifice, does prohibit salvation on the basis of performance, cultic or otherwise (cf. Isa. 1:3-5). Whether one is reading the Old Testament or the New Testament, a redemptive approach to God is always via God’s grace. This is even more clearly true when one is referring to the eschatological salvation, that is, the telos of God’s covenantal plans.
 Shortly afterwards we read about what at first sight looks like a contradiction. God says to Moses that “I appeared to Abraham, to Isaac, and to Jacob, as God Almighty, but by My name LORD I was not known to them.” (Exod. 6:3). Of course, God had used that name and Abraham knew and used it in addressing God (e.g. Gen. 13:4; 14:22; 15:2, 8). But what was not made clear was the significance of the Name. I don’t agree with the view that the editor of the Pentateuch retroactively placed the Tetragrammaton onto the lips of Abraham (e.g. Robin Routledge, Old Testament Theology, 92-94). Childs seems to argue similarly, although he does notice that the context lays stress upon the character of God and not the name itself. – Brevard S. Childs, Exodus, 112-115.
By contrast, Garrett believes “one could hardly more badly misread the text than to claim that Exod. 6 is the revelation of something new.” – Duane A. Garrett, A Commentary on Exodus, 252-253. In his view God was saying that He was to be now known under the name YHWH. But Motyer is surely correct when he says that “the character expressed by the name that was withheld from the patriarchs and not the name itself.” – J. Alec Motyer, The Revelation of the Divine Name, 15-16. On top of this see Allen P. Ross, “Did the Patriarch’s Know the Name of the LORD?” in David M. Howard Jr. & Michael A. Grisanti, eds, Giving the Sense: Understanding and Using Old Testament Historical Texts, 323-339
 Kaiser observes, “The connection is undeniable. The duty of obedience (law, if you wish) was intimately ted up with promise as a desired sequel. Therefore, the transition to the coming time of Mosaic law should not be all that difficult for any who had really adequately listened to the full revelation of the promise in the patriarchal era. But in no way was the promise-plan dependent on anyone’s obedience; it only insured their participation in the benefits of the promise but not on its maintenance.” – Walter C. Kaiser, Jr, The Promise-Plan of God, 61.
 “Ultimately, the people had to look to God for forgiveness and could not expect pardon by mechanically fulfilling the external requirements (Isa. 1:11-17; Mic. 7:18-20).” – Willem VanGemeren, The Progress of Redemption, 162