So it is clear that without grace man cannot rise to the highest knowledge and the purest love of which he is capable in this life; far less can he reach that final and perfected blessedness which is expected hereafter. For this he must possess the virtue of Faith, which comes not without grace.
“The perfection of the rational creature consists not only in that which may be his, in accordance with his nature; but also in that which may come to him from some supernatural sharing in the divine goodness. The final beatitude of man consists in some supernatural vision of God. Man can attain to that only through some mode of learning from God the Teacher, and he must believe God as a disciple believes his master” (Pars II. ii., Qu. ii. Art. 3).
Within the province of the Christian Faith “it is necessary that man should accept per modum fidei not only what is above reason, but also what may be known through reason.” (Art. 4). He must believe explicitly the prima credibilia, that is to say, the Articles of Faith; it is enough if he believes other credibilia implicitly, by holding his mind prepared to accept whatever Scripture teaches (Art. 5).
“To believe is an act of the intellect (actus intellectus) as moved by will to assenting. It proceeds from the will and from the intellect.... Yet it is the immediate act of the intellect, and therefore faith is in the intellect as in a subject [i.e. possessor]” (Qu. iv. Art. 2).
And Thomas, having shown the function of will in any act of faith, passes on by the same path to connect fides with caritas:
“Voluntary acts take their species from the end which is the object of volition. That from which anything receives its species, occupies the place held by form in material things. Hence, as it were, the form of any voluntary act is the end to which it is directed (ordinatur). Manifestly, an act of faith is directed to the object willed (which is the good) as to an end. But good which is the end of faith, to wit, the divine good, is the proper object of caritas. And so caritas is called the form of faith, in so far as through caritas the act of faith is perfected and given form” (Qu. iv. Art. 3).
Thomas makes his conclusion more precise:
“As faith is the consummation of the intellect, that which pertains to the intellect, pertains, per se, to faith. What pertains to will, does not, per se, pertain to faith. The increment making the difference between the faith which has form and faith which lacks it (fides formata, fides informis), consists in that which pertains to will, to wit, to caritas, and not in what pertains to intellect” (Qu. iv. Art. 4).
Only the fides which is formed and completed in caritas is a virtue (Art. 5). And Thomas says concisely (Qu. vi. Art. 1) what in many ways has been made evident before: For Faith, it is necessary that the credibilia should be propounded, and then that there should be assent to them; but since man, in assenting to those things which are of the Faith, is lifted above his nature, his assent must proceed from a supernatural principle working within him, which is God moving him through grace.
It is not hard to see why two gifts (dona) of the Holy Spirit should belong to the virtue Faith, to wit, understanding and knowledge, intellectus et scientia. Thomas gives the reasons in an argument germane to his Aristotelian theory of cognition: