The Living God
From the Catechism of the Catholic Church, Simplified
The God of History (205)
God identified himself to Moses as the God who guided the Patriarchs (Abraham, Isaac, and Jacob). God keeps his promises that he would act within human history.
The Mysterious Name (206-207)
Moses said, "If the people of Israel ask me What is his name?' what shall I say to them?" God said to Moses, "I AM WHO AM" and "Say to this people of Israel, I Am has sent me to you'" (Ex 3:13-15). Although clearly revealed, this name shows that God is hidden yet always close to men. His name shows faithfulness because he was there in the past (the God of your fathers) and he will always be there. "I will be with you" (Ex 3:6, 12).
Awe and Respect (208-209)
In God's mysterious presence, Moses saw his own insignificance. Others, like Isaiah ("Woe is me! I am lost" - Isa 6:5) and Peter ("Depart from me, O Lord, I am a sinful man" - Lk 5:8) had the same experience of awe in God's presence.
Out of respect, Israel did not pronounce the word "Yahweh" but used instead "Adonai" meaning "Lord." Christians used this word "Lord" to affirm Jesus' divinity. "Jesus Christ is Lord" (Phil 2:11).
God - Forgiving and Merciful (210-211)
After Israel sinned, God agreed to remain with them (Ex 32-33). He even showed that he was a forgiving God, "a God merciful and gracious" (Ex 34:6). God's name "I Am" shows his faithfulness. By sending his Son, God is "rich in mercy" (Eph 2:4). Jesus had the same divine name: "Then you will realize that I Am'" (Jn 8:28).
No Beginning or End (212-213)
Over the centuries, Israel realized that God had no end: "Your years have no end" (Ps 102:26-27). James writes that in the Father, there is "no variation or shadow due to change" (1:17). "I am" means that God alone "is." He has no beginning and no end and from him all creatures receive their existence.