- To you it was shown that you might know that the Lord, He is God; there is no other besides Him. - Deuteronomy 4:35
- yet for us there is but one God, the Father, from whom are all things and we exist for Him; and one Lord, Jesus Christ, by whom are all things, and we exist through Him. - 1 Corinthians 8:6
- For there is one God, and one mediator also between God and men, the man Christ Jesus, - 1 Timothy 2:5
Besides the many Biblical prooftexts supporting monotheism, there are three key arguments support monotheism.
First, a study of world religions demonstrates that at their roots, they began as monotheistic, before devolving into polytheism. Each of these religions share a set of common truths: one God who is personal, omniscient, and omnipotent, who created the world, is the author of morality, and provides reconciliation to those who disobey Him. That these religions share these common truths demonstrates that monotheism is foundational to humanity’s belief in God.
Second, the universe demands one God who orders and sustains the universe. If more than one God existed, it would result in chaos and disorder in the universe. Such chaos and disorder would be the result of each competing deity’s authority and choice.
Third, God is a perfect being. Perfection means that God lacks nothing in His character or attributes. In other words, God is complete, full, wanting in nothing. Therefore, for another deity to exist, it would have to be different from God. Anything different from perfect is less than perfect.