What does all the rest of the Old Testament and the New Testament rest on?
All the rest of the Old Testament, from Genesis 12 onward, and the New Testament rest on the Abrahamic covenant. That covenant promised the line of Abraham and David would produce an eternal royal government and kingdom ruled by the King of Kings, a benevolent monarchy that is righteous, fair, and glorious.
Les teaches that David becomes the beginning of the royal family that will lead not only through generations of this existence but all the way into eternity. Out of the line of Abraham and David would come this government, and it will not be a democracy but a monarchy, ruled by the King of Kings and Lord of Lords. He will not be a despot or a totalitarianist but a benevolent ruler, and His kingdom will be righteous, fair, and glorious. This was the prospect laid out in the Abrahamic covenant. Les explains that all the rest of the Old Testament, from Genesis 12 right on into the New Testament, is resting on this covenant. There will be other covenants, such as the covenant with Moses called the Law, and the covenant with Moses and Israel that even though they are uprooted from the land they will be brought back to it as their homeland. Along with that, God promises David a royal family leading up to the King and the government.