What is a covenant, and why can it never be changed or withdrawn?
A covenant is an agreement that God made, like the Abrahamic, Davidic, and Law covenants. It can never be changed or withdrawn because God Himself made it, so it settles forever and remains permanently fixed once confirmed in the person of Christ.
Les explains that 'covenant' is an important word all through the Old Testament. He identifies the Law as a covenant, just as the Abrahamic covenant and the Davidic covenant were covenants. A covenant is an agreement God made, and because God made it, He could never change or withdraw it; it settled forever. Paul speaks of the covenant confirmed before of God in the person of Christ. The Law came 430 years after the promise to Abraham that out of him would come the seed, when Israel came out of Egypt and received the Law at Sinai. Les also notes the numbers 430, 400, and 490 years appear, but there is no contradiction.
And this I say, that the covenant, that was confirmed before of God in Christ, the law, which was four hundred and thirty years after, cannot disannul, that it should make the promise of none effect.