Summa contra Gentiles1.38 Chapter XXXVIII. That God is goodness itself

From the above we are able to conclude that God is His own goodness.

For to be in act is for every thing its own good. Now, God is not only being in act, but is His own being, as proved above.” Therefore He is goodness itself and not merely good.

Further. The perfection of a thing is its goodness, as we have shown above. Now the perfection of the divine being does not consist in something added thereto, but in its being perfect in itself, as proved above.’ Therefore God’s goodness is not something added to His essence, but His essence is His goodness.

Again. Any good that is not its own goodness is good by participation. Now that which is by participation presupposes something antecedent to itself, from which it derives the nature of goodness. But it is not possible to continue thus to infinity: since in final causes there is no proceeding to infinity, for the infinite is inconsistent with finality: and the good has the nature of an end. We must therefore come to some first good, that is good not by participation in relation to something else, but by its essence. Now this is God. Therefore God is His own goodness.

Again. That which is can participate something, but being itself can participate nothing: because that which participates is potentiality, whereas being is act. Now, God is being itself, as we have proved.’ Therefore He is good not by participation, but essentially.

Moreover. In every simple thing, being and that which is are one: for if they be distinct, there is no longer simplicity.?, Now, God is absolutely simple, as we have proved. Therefore that He is good is not distinct from Himself. Therefore He is His own goodness.

These same arguments show that nothing else is its own goodness: hence it is said (Matth. xix. 17): None is good but God alone.