(Author: Norman Geisler)
How can God be three and yet one? Isn’t this a contradiction? It would seem that God could be one and not three, or three and not one. But he cannot be both three and one at the same time. It would be a violation of the most fundamental law of thought, namely, the law of noncontradiction.
First of all, the Christian belief in a Trinity of three persons in one God is not a contradiction. A contradiction occurs only when something is both A and non-A at the same time and in the same sense. God is both three and one at the same time but not in the same sense. He is three persons but one in essence. He is three persons but only one in nature.
It would be a contradiction to say that God had three natures in one nature or three persons in one person. But it is not a contradiction to claim that God has three persons in one nature. God is like a triangle. At the same time it has three corners and yet it is only one triangle. Each corner is not the same as the whole triangle. Or, God is like one to the third power. 1 x 1 x 1 = 1. God is not 1 + 1 + 1 + = 3, which is tritheism or polytheism. God is one God, manifested eternally and simultaneously in three distinct persons.
God is love (1 John 4:16). But to have love, there must be a lover (Father), a loved one (Son), and a spirit of love (Holy Spirit). So, love itself is a tri-unity.
Another illustration of the Trinity is that God is like my mind, ideas, and words. There is a unity between them, yet they are distinct from each other.
Of course, the Trinity is a mystery. It goes beyond reason without going against reason. We can apprehend it, but we cannot completely comprehend it. As someone wisely said, “If we try to understand God completely, we may lose our mind, but if we do not believe in the Trinity sincerely, we will lose our soul!”