That in God Existence and Essence is the same*

IT has been shown above (Chap. XV, n. 4) that there is an Existence which of itself necessarily is; and that is God. If this existence, which necessarily is, is contained in some essence not identical with it, then either it is dissonant and at variance with that essence, as subsistent existence is at variance with the essence of whiteness; or it is consonant with and akin to that essence, as existence in something other than itself is consonant with whiteness. In the former case, the existence which of itself necessarily is will not attach to that essence, any more than subsistent existence will attach to whiteness. In the latter case, either such existence must depend on the essence, or both existence and essence depend on another cause, or the essence must depend on the existence. The former two suppositions are against the idea of a being which of itself necessarily is; because, if it depends on another thing, it no longer is necessarily. From the third supposition it follows that that essence is accidental and adventitious to the thing which of itself necessarily is; because all that follows upon the being of a thing is accidental to it; and thus the supposed essence will not be the essence at all. God therefore has no essence that is not His existence.

2. Everything is by its own existence. Whatever then is not its own existence does not of itself necessarily exist. But God does of Himself necessarily exist: therefore God is His own existence.

4. 'Existence' denotes a certain actuality: for a thing is not said to 'be' for what it is potentially, but for what it is actually. But everything to which there attaches an actuality, existing as something different from it, stands to the same as potentiality to actuality. If then the divine essence is something else than its own existence, it follows that essence and existence in God stand to one another as potentiality and actuality. But it has been shown that in God there is nothing of potentiality (Chap. XVI), but that He is pure actuality. Therefore God's essence is not anything else but His existence.*

5. Everything that cannot be except by the concurrence of several things is compound. But nothing in which essence is one thing, and existence another, can be except by the concurrence of several things, to wit, essence and existence. Therefore everything in which essence is one thing, and existence another, is compound. But God is not compound, as has been shown (Chap. XVIII). Therefore the very existence of God is His essence. This sublime truth was taught by the Lord to Moses (Exod. iii, 13, 14) If they say to me, What is his name? what shall I say to them? Thus shalt thou say to the children of Israel: He who is hath sent me to you: showing this to be His proper name, He who is. But every name is given to show the nature or essence of some thing. Hence it remains that the very existence or being of God is His essence or nature.

1.21 : That God is His own Essence
1.23 : That in God there is no Accident