The one absolutely and infinitely perfect spirit who is the Creator of all. In the definition of the First Vatican Council, fifteen internal attributes of God are affirmed, besides his role as Creator of the universe: "The holy, Catholic, apostolic Roman Church believes and professes that there is one true, living God, the Creator and Lord of heaven and earth. He is almighty, eternal, beyond measure, incomprehensible, and infinite in intellect, will and in every perfection. Since He is one unique spiritual substance, entirely simple and unchangeable, He must be declared really and essentially distinct from the world, perfectly happy in Himself and by his very nature, and inexpressibly exalted over all things that exist or can be conceived other than Himself" (Denzinger 3001).
Reflecting on the nature of God, theology has variously identified what may be called his metaphysical essence, i.e., what is God. It is commonly said to be his self-subsistence. God is Being Itself. In God essence and existence coincide. He is the Being who cannot not exist. God alone must be. All other beings exist only because of the will of God.