God is not composed or divisible by any physical or metaphysical means. Simplicity of God refers to the fact that he has no parts. The simplicity teaching extends to the entire nature of God. His substance, nature, and very being is that of utter simplicity. The properties usually attributed to God such as omnipotence, omniscience and omnipresence do not contradict the teaching of simplicity because each property is a different way of looking at the infinite active being of God from a limited perspective. One consequence of this teaching is the fact that since God is simple, he must be a pure spirit.
Philosophical Proof from St. Thomas Aquinas’ Summa Theologica
Primary Argument:
P1. Every composite must have potentiality and actuality
P2. God is entirely actual.
C1. God is not composite and therefore simple.
God is Simple