(CG 3/155). Of Graces given gratuitously (Book 3. God, the End of Creatures) (Summa Contra Gentiles) (Aquinas, Thomas, St.)

THE power of free will regards matters of election: but a matter of election is some particular thing to be done; and a particular thing to be done is what is here and now: but perseverance is not a matter of present and immediate conduct, but a continuance of activity for all time: perseverance therefore is an effect above the power of free will, and therefore needing the assistance of divine grace.

3. Though man is master of his act, he is not master of his natural powers; and therefore, though he is free to will or not will a thing, still his willing cannot make his will in the act of willing adhere immovably to the thing willed or chosen. But the immovable adherence of the will to good is requisite for perseverance: perseverance therefore is not in the power of free will.

Hence it is said: He who hasbegun a good work in you will perfect it unto the day of Christ Jesus (Philip. i, 6): The God of all grace, who hascalled us to his eternal glory in Christ Jesus, himself will perfect us through some little suffering, confirm and establish us (1 Pet. v, 10). There are also found in Holy Scripture many prayers for perseverance: e.g., Perfect my steps in your ways, that my footsteps may not slip (Ps. xvi, 5); and especially that petition of the Lord's Prayer, Your kingdom come: for the kingdom will not come for us unless we persevere in good.

Hereby is refuted the error of the Pelagians, who said that free will is sufficient for man for his perseverance in good, and that there is no need of the assistance of grace for the purpose.

As free will is not sufficient for perseverance in good without the help of God given from without, so neither is any infused habit. For in the state of our present life the habits infused into us of God do not totally take away from our free will its fickleness and liability to evil, although they do to some extent establish the free will in good. And therefore, when we say that man needs the aid of grace for final perseverance, we do not mean that, over and above the habitual grace first infused into him for the doing of good acts, there is infused into him another habitual grace enabling him to persevere; but we mean that, when he has got all the gratuitous habits that he ever is to have, man still needs some aid of divine providence governing him from without.