Of God and His Creatures3. It is by will that man is directed to a final end: for the good and the final end is the object of will. And the divine assistance is vouchsafed us for this special purpose, that we may attain to our final end. That aid therefore does not exclude the act of our will: on the contrary, it is precisely the act of our will that the divine assistance produces in us: hence the Apostle says: It is God who worketh in us both to will and to act according to the good will (Phil. ii, 13). But compulsion defeats in us the act of the will: for we do that under compulsion of which we will the contrary.
4. Man arrives at his last end by acts of virtue. But acts done under compulsion are not acts of virtue, for in virtue the chief thing is choice.
Hence it is said: Consider that to-day the Lord hath put forth in thy sight life and good, and on the other hand death and evil, that thou mayest love the Lord thy God and walk in his ways. But f thy heart is turned away, and thou wilt not hear, etc. (Deut. xxx, 15-18): Before man is life and death, good and evil: what pleases him shall be given to him (Ecclus xv, 18).
3.148 : That Man stands in need of Divine Grace for the Gaining of Happiness
3.150 : That Man cannot merit beforehand the said Assistance