Summa contra Gentiles1.37 Chapter XXXVII. That God is good

The goodness of God may be concluded from His perfection which we have proved.

For that by reason of which a thing is said to be good is its own virtue, since the virtue of any thing is that which makes its subject good and renders its work good. Now virtue is a perfection: since we say that a thing is perfect when it attains its proper virtue, as stated in 7 Phys. Wherefore a thing is good from the fact of its being perfect: and consequently every thing desires its own perfection as its proper good. Now it has been proved that God is perfect. Therefore He is good.

Again. It has been proved above that there is an immovable first mover which is God. Now He moves as a mover absolutely immovable: and this moves as the object of desire. Wherefore God, since He is the first immovable mover, is the first object of desire. Now a thing is desired in two ways, either because it is good, or because it seems good. The former is that which is good, for the seeming good does not move per se, but according as it has some appearance of good; whereas the good moves per se. Therefore the first object of desire, Which is God, is good.

Further. The good is that which all things desire, which the Philosopher quotes as very well said. Now all things desire to be in act according to their mode: which is evident from the fact that every thing, by its nature, shrinks from corruption. Wherefore the essential notion of the good is to be in act, and consequently evil which is opposed to good results from the privation of act by potentiality, as the Philosopher declares (9 Metaph.). Now God is a being in act and not in potentiality, as we have proved above. Therefore He is truly good.

Moreover. The bestowal of being and goodness proceeds from goodness. This is proved from the very nature of the good, and from the notion it conveys. For the good of a thing is naturally its act and perfection. Now a thing acts through being in act: and by acting it bestows being and goodness on other things. Wherefore it is a sign of a thing's perfection that it is able to produce its like, as the Philosopher declares (4 Meteor.). Again, the notion of the good is that it is something appetible: and this is an end. And the end moves the agent to act. Hence good is said to be diffusive of self and being. Now, this diffusion is becoming to God: for it has been shown above that He is the cause of being in other things, since He is the per se necessary being. Therefore He is truly good.

Wherefore it is said in the psalm: How good is God to Israel, to them that are of a right heart; and (Lam. iii. 25): The Lord is good to them that hope in Him, to the soul that seeketh Him.