CATECHISM OF THE CATHOLIC CHURCH
SECOND EDITION

Paragraphs 207–211

207 By revealing his name God at the same time reveals his faithfulness which is from everlasting to everlasting, valid for the past ("I am the God of your father"), as for the future ("I will be with you"). God, who reveals his name as "I AM", reveals himself as the God who is always there, present to his people in order to save them.
208 Faced with God's fascinating and mysterious presence, man discovers his own insignificance. Before the burning bush, Moses takes off his sandals and veils his face in the presence of God's holiness. Before the glory of the thrice-holy God, Isaiah cries out: "Woe is me! I am lost; for I am a man of unclean lips." Before the divine signs wrought by Jesus, Peter exclaims: "Depart from me, for I am a sinful man, O Lord." But because God is holy, he can forgive the man who realizes that he is a sinner before him: "I will not execute my fierce anger. . . for I am God and not man, the Holy One in your midst." The apostle John says likewise: "We shall. . . reassure our hearts before him whenever our hearts condemn us; for God is greater than our hearts, and he knows everything."
209 Out of respect for the holiness of God, the people of Israel do not pronounce his name. In the reading of Sacred Scripture, the revealed name (YHWH) is replaced by the divine title "LORD" (in Hebrew Adonai, in Greek Kyrios). It is under this title that the divinity of Jesus will be acclaimed: "Jesus is LORD."
210 After Israel's sin, when the people had turned away from God to worship the golden calf, God hears Moses' prayer of intercession and agrees to walk in the midst of an unfaithful people, thus demonstrating his love. When Moses asks to see his glory, God responds "I will make all my goodness pass before you, and will proclaim before you my name 'the LORD' [YHWH]." Then the LORD passes before Moses and proclaims, "YHWH, YHWH, a God merciful and gracious, slow to anger, and abounding in steadfast love and faithfulness"; Moses then confesses that the LORD is a forgiving God.
211 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". By going so far as to give up his own Son for us, God reveals that he is "rich in mercy". By giving his life to free us from sin, Jesus reveals that he himself bears the divine name: "When you have lifted up the Son of man, then you will realize that 'I AM'."