Objection 1. It would seem that faith, hope, and charity are not fittingly reckoned as three theological virtues. For the theological virtues are in relation to Divine happiness, what the natural inclination is in relation to the connatural end. Now among the virtues directed to the connatural end there is but one natural virtue, viz. the understanding of principles. Therefore there should be but one theological virtue.
Objection 2. Further, the theological virtues are more perfect than the intellectual and moral virtues. Now faith is not reckoned among the intellectual virtues, but is something less than a virtue, since it is imperfect knowledge. Likewise hope is not reckoned among the moral virtues, but is something less than a virtue, since it is a passion. Much less therefore should they be reckoned as theological virtues.
Objection 3. Further, the theological virtues direct man's soul to God. Now man's soul cannot be directed to God, save through the intellective part, wherein are the intellect and will. Therefore there should be only two theological virtues, one perfecting the intellect, the other, the will.
On the contrary, The Apostle says (1 Corinthians 13:13): "Now there remain faith, hope, charity, these three."
I answer that, As stated above (Article 1), the theological virtues direct man to supernatural happiness in the same way as by the natural inclination man is directed to his connatural end. Now the latter happens in respect of two things. First, in respect of the reason or intellect, in so far as it contains the first universal principles which are known to us by the natural light of the intellect, and which are reason's starting-point, both in speculative and in practical matters. Secondly, through the rectitude of the will which tends naturally to good as defined by reason.
But these two fall short of the order of supernatural happiness, according to 1 Corinthians 2:9: "The eye hath not seen, nor ear heard, neither hath it entered into the heart of man, what things God hath prepared for them that love Him." Consequently in respect of both the above things man needed to receive in addition something supernatural to direct him to a supernatural end. First, as regards the intellect, man receives certain supernatural principles, which are held by means of a Divine light: these are the articles of faith, about which is faith. Secondly, the will is directed to this end, both as to that end as something attainable--and this pertains to hope--and as to a certain spiritual union, whereby the will is, so to speak, transformed into that end--and this belongs to charity. For the appetite of a thing is moved and tends towards its connatural end naturally; and this movement is due to a certain conformity of the thing with its end.
Reply to Objection 1. The intellect requires intelligible species whereby to understand: consequently there is need of a natural habit in addition to the power. But the very nature of the will suffices for it to be directed naturally to the end, both as to the intention of the end and as to its conformity with the end. But the nature of the power is insufficient in either of these respects, for the will to be directed to things that are above its nature. Consequently there was need for an additional supernatural habit in both respects.
Reply to Objection 2. Faith and hope imply a certain imperfection: since faith is of things unseen, and hope, of things not possessed. Hence faith and hope, in things that are subject to human power, fall short of the notion of virtue. But faith and hope in things which are above the capacity of human nature surpass all virtue that is in proportion to man, according to 1 Corinthians 1:25: "The weakness of God is stronger than men."
Reply to Objection 3. Two things pertain to the appetite, viz. movement to the end, and conformity with the end by means of love. Hence there must needs be two theological virtues in the human appetite, namely, hope and charity.
Source: Summa Theologica (New Advent)