Why do we believe in only one God?
We believe in only one God because, according to the testimony of Sacred Scripture, there is only one God and, according to the laws of logic, there can be only one.
If there were two gods, then the one god would be a limit on the other; neither of the two would be infinite, neither one perfect; in these respects neither of the two would be God. Israel’s fundamental experience of God is: “Hear, O Israel: The Lord our God is one Lord” (Deut 6:4). Again and again the prophets exhort the people to abandon their false gods and to convert to the one God: “For I am God, and there is no other” (Is 45:22).
Why does God give himself a name?
God gives himself a name so as to make it possible to address him.
God does not wish to remain incognito. He does not want to be revered as a “higher being” that is merely sensed or surmised. God wishes to be known and to be called upon as someone real and active. In the burning bush God reveals to Moses his holy name: Yhwh (Ex 3:14). God makes it possible for his people to address him, but he still remains the hidden God, the present mystery. Out of reverence for God, the name of God was not (and is not) spoken in Israel; the title Adonai (Lord) is substituted. This same word is used by the New Testament when it glorifies Jesus as true God: “Jesus is Lord!” (Rom 10:9).