Read the series so far.
The Mosaic Covenant as a Historical Placeholder for Other Covenants
If the commandments in the “Ten Words” on Sinai (Exod. 20) and all those that followed in their train were too stringent for a fallen people to keep, at least the covenant God made with Israel, and which they voluntarily entered into (in Exod. 24), distinguished them among the other nations of the world. It did this to the extent that they were preserved as a distinct people in continuity with Abraham, Isaac and Jacob.1
Just as the Noahic covenant guarantees the perpetuation of the regulation and predictability of the rhythms of nature, thereby creating the stage of history for God’s program to play out upon, the Mosaic covenant acts to set the covenants with David and Phinehas within a theocratic outlook—even if both of these covenants transcend the temporary “old covenant” and are embraced by the coming New covenant. Another way to say this is to imagine the people of Israel as connecting the Mosaic covenant to the New covenant brought upon Israel at Christ’s return (Isa. 61:2b-3; Jer. 31:31-37); a covenant that supersedes the old one, but without morphing the promises God made out of all recognition.