Catechism of the Catholic Church §211 — excerpt
The divine name, "I Am" or "He Is", expresses God's faithfulness: despite the faithlessness of men's sin and the punishment it deserves, he keeps "steadfast love for thousands".
This translation is under copyright, so only the cited words are quoted here. Follow the link for the full text. Translation: English translation of the Catechism of the Catholic Church, 2nd ed. (Libreria Editrice Vaticana), as posted at vatican.va.