Commentaria in Summam contra Gentiles, Liber I

From the foregoing, Saint Thomas draws two corollaries¹.

The first of which is: God cannot will evil. And this is understood of evil formally, insofar as it is evil, and under the aspect of evil: as is clear from the First Part, q. 19, a. 9.

It is proved first. Every divine operation is an operation of power, since God's power is his essence. Therefore God cannot will evil.

Note that, although the divine essence and its power, say charity, are distinguished by reason, they are nevertheless one in reality. And therefore an operation cannot proceed from the essence without proceeding from the power. And thus in the act of divine operation evil cannot arise on account of any defect in the active principle.

Second. In the divine cognition, error cannot exist. Therefore neither can His will tend toward evil. — The consequence is proved: because the will is never carried toward evil except when error exists in reason, at least in the particular object of choice, while it judges some evil to be good for the moment and proposes it to the will.

Third. God is the highest good. Therefore, etc. — The consequence is evident. For the highest good admits of no partnership with evil, just as what is supremely hot admits no admixture of cold.

Fourth. The divine will cannot be turned away from the end, since it can will nothing except by willing itself. Therefore etc. — The inference is proved: because, since the good has the character of an end, evil cannot enter into the will except through a turning away from the end.

It is confirmed by Deuteronomy 32 and Habakkuk 1.

From this, too, the error of the Jews and of the Luciferians is refuted.

Concerning that proposition, "The good has the character of an end," it should be noted that it has truth of that which is good first and per se, as is said in Verit., q. XXI, a. 1². — It can also be understood of the good from which the act of the will first has it that it be good, etc.