דברי הימים א, פרק ט״ז, פסוק י״ז

A promise made by God carries immense weight, and establishing it as a permanent reality gives it eternal stability. The primary approach among commentators is that God took His earlier oath and firmly grounded it, making it an enduring and valid decree. He set this promise for Jacob as a fixed law, establishing a reality that is completely immune to change.

To ensure this permanence is fully understood, the concept is presented twice. The promise is framed both as a fixed law for Jacob and as an everlasting covenant for the Israelites. This is a deliberate repetition of the exact same idea using different terms. It serves to strongly emphasize that the oath established for the people is an eternal agreement that will never fade.