The nature of God is paramount in apologetics, so today we will continue to explore what that nature entails. The article below explains God’s unity:
Unity. Classical theists have offered three reasons for God’s unity (ibid., 1a.11.3). The first argument is from the simplicity of God. An absolutely simple being cannot be more than one, since to be more than one there must be parts, but simple beings have no parts. Absolutely simple beings are not divisible. God is an absolutely simple being. Therefore, God cannot be more than one being.
God’s perfection argues for his unity. If two or more gods existed, they would have to differ. In order to differ, one must have what the other lacks. But an absolutely perfect being cannot lack anything. Therefore, there can only be one absolutely perfect being. God’s unity also can be inferred from the unity of the world. The world is composed of diverse things. Diverse things do not come together unless they are ordered. But the world has an ordered unity. Therefore, there must be one Orderer of the world.
Theists argue that essential unity is better explained by one Orderer than by many orderers. For one is the essential cause of oneness, but many is only the accidental cause of oneness. Therefore, it is reasonable to infer that there is only one cause of the world, not many.