The Predestination of the Saints/Gift of Perseverance

And, therefore, commending that grace which is not given according to any merits, but is the cause of all good merits, he says, “Not that we are sufficient to think anything as of ourselves, but our sufficiency is of God.” Let them give attention to this, and well weigh these words, who think that the beginning of faith is of ourselves, and the supplement of faith is of God. For who cannot see that thinking is prior to believing? For no one believes anything unless he has first thought that it is to be believed.

For however suddenly, however rapidly, some thoughts fly before the will to believe, and this presently follows in such wise as to attend them, as it were, in closest conjunction, it is yet necessary that everything which is believed should be believed after thought has preceded; although even belief itself is nothing else than to think with assent. For it is not every one who thinks that believes, since many think in order that they may not believe; but everybody who believes, thinks—both thinks in believing and believes in thinking.

Therefore in what pertains to religion and piety (of which the apostle was speaking), if we are not capable of thinking anything as of ourselves, but our sufficiency is of God, we are certainly not capable of believing anything as of ourselves, since we cannot do this without thinking; but our sufficiency, by which we begin to believe, is of God. Wherefore, as no one is sufficient for himself, for the beginning or the completion of any good work whatever—and this those brethren of yours, as what you have written intimates, already agree to be true, whence, as well in the beginning as in the carrying out of every good work, our sufficiency is of God—so no one is sufficient for himself, either to begin or to perfect faith; but our sufficiency is of God.

Because if faith is not a matter of thought, it is of no account; and we are not sufficient to think anything as of ourselves, but our sufficiency is of God.