Harvard professor and distinguished Jewish scholar Jon D. Levenson wrote a fabulous book, Sinai & Zion: An Entry into the Jewish Bible, in which he talks about the Sinaitic and Davidic covenants, among other things. One fascinating aspect is that he finds Mendenhall and Weinfeld’s studies on suzerainty treaties and covenant of grants in the ancient Near East helpful; Levenson utilizes the parallels between the ANE treaties and those found in the Hebrew Bible. Here are his own words:
“Moshe Weinfeld identified over a decade ago a type of covenant which he calls the ‘covenant of grant,’ to distinguish it from the type we saw in Part I (my note: the suzerainty treaty), which Weinfeld terms the ‘treaty.’ ‘…While the grant is a reward for loyalty and good deeds already performed,’ he writes, ‘the treaty is an inducement for future loyalty.'”
“In the case of the grant to David, the ancestor has already satisfied what claims YHWH might wish to make upon his line. YHWH reciprocates by granting David an endless dynasty. It is the suzerain (God) who is now under oath. He swears to reward David with the gift of a continuing dynasty. The same pattern appears elsewhere in the Bible as well, especially in the cases of Noah, Abraham, Caleb, and Phinehas.”
Levenson is clear later: “This Davidic covenant, then, is distinct in kind from the Sinaitic.” The Davidic covenant, he notes, is “suprahistorical.” “…Since the focus is upon the constancy of God rather than the changeability of man, it brings to light what is secure and inviolable, whereas the Sinaitic texts tend to emphasize the precariousness of life and the consequent need for a continuously reinvigorated obedience.”
This is helpful, especially as we consider the covenant of works and the covenant of grace.
The above quotes are found in Jon D. Levenson, Sinai & Zion (New York: HarperCollins Publishers, 1985), 100-1.