What is the principle that governs how God's promises and covenants work?
The principle is that God's promises and covenants originate and conclude in God Himself. They are not dependent on human faithfulness or weakness. Because they begin with God and end with God, human failures cannot break them. God is sovereign and fulfills His purposes according to His own good pleasure.
Les explains that everything begins and ends in and with God. He applies this especially to the Old Testament covenants: when God made the covenant with Abraham, the weaknesses of the nation of Israel and the children of Abraham did not break it, because it began with God and it is going to end with God. Les says the same is true of all the promises of Scripture—they begin and they end in God Himself. He also notes that God is sovereign and can do things any way He sees fit, keeping things secret if He chooses, until He revealed many of these things to the Apostle Paul, according to His good pleasure.