Catechism of the Catholic Church
212 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. 24
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." 25
In God "there is no variation or shadow due to change." 26 God is "HE WHO IS", from everlasting to everlasting, and as such remains ever faithful to himself and to his promises.
213 The revelation of the ineffable name "I AM WHO AM" contains then the truth that God alone IS. The Greek Septuagint translation of the Hebrew Scriptures, and following it the Church's Tradition, understood the divine name in this sense: God is the fullness of Being and of every perfection, without origin and without end. All creatures receive all that they are and have from him; but he alone is his very being, and he is of himself everything that he is.
English Translation of the Cathechism of the Catholic Church for the United States of America © 1997, United States Catholic Conference, Inc.