Divine grace
According to Thomas Aquinas, faith is "the act of the intellect assenting to a Divine truth owing to the movement of the will, which is itself moved by the grace of God" (St. Thomas, II-II, Q. iv, a. 2). And just as the light of faith is a gift supernaturally bestowed upon the understanding, so also this Divine grace moving the will is, as its name implies, an equally supernatural and an absolutely gratuitous gift. Neither gift is due to previous study, neither of them can be acquired by human efforts, but "Ask and ye shall receive." Because the virtue is "infused" and not reachable by human efforts, it is therefore one of the theological virtues.