Christianity is a monotheistic faith, as is Judaism and Islam. Jesus taught us, in Mark 12:29-30, “The Lord our God, the Lord is one; and you shall love the Lord your God with all your heart, and with all your soul, and with all your mind, and with all your strength.”
But what makes this affirmation so important? Why should we believe in only ONE God? I answer very simply: According to Holy Scripture and Jesus himself there is only ONE God. And according to all logic if there were two gods, then one god would be a limit on the other. Neither could be infinite and neither would be the true God. The experience of Israel is clear on this point: “Hear, O Israel: The Lord our God is one Lord” (Deuteronomy 6:4).
I recently read through the entire Old Testament in the course of two months. I was struck by many common themes but none is more obvious than this one – the law and the prophets continually exhort Israel that God (Yahweh) is the true and only God. “For I am God, and there is no other” (Isaiah 45:22).
The term monotheism comes from two Greek words: (1) manos, which means only, and (2) theos, which means God. Monotheism is the doctrine about the existence of the one, true God. Monotheism teaches that God is unique, absolute, and personal. He is the ultimate ground of everything that exists because he is the one, true and only God.
No truth is more basic to living and personal faith. Deny monotheism and you will never have a robust faith in the living and true God. It is not an accident that the first affirmation of the Nicene Creed is: “I believe in one God . . .” Do you really believe this most basic of all faith affirmations? It makes a huge difference in life if you do. As our culture drifts off into polytheism and Gnosticism, at least practically speaking, it is absolutely essential for Christians to remain clear on the most basic of all truths.