God alone IS
Over the centuries, Israel's faith was able to manifest and deepen realization of the riches contained in the revelation of the divine name. God is unique; there are no other gods besides him.
He transcends the world and history. He made heaven and earth: "They will perish, but you endure; they will all wear out like a garment....but you are the same, and your years have no end."
In God "there is no variation or shadow due to change." God is "HE WHO IS", from everlasting to everlasting, and as such remains ever faithful to himself and to his promises.
Source: Catechism of the Catholic Church (Vatican.va)