Objection 1. It would seem that charity is not the greatest of the theological virtues. Because, since faith is in the intellect, while hope and charity are in the appetitive power, it seems that faith is compared to hope and charity, as intellectual to moral virtue. Now intellectual virtue is greater than moral virtue, as was made evident above (Question 62, Article 3). Therefore faith is greater than hope and charity.
Objection 2. Further, when two things are added together, the result is greater than either one. Now hope results from something added to charity; for it presupposes love, as Augustine says (Enchiridion viii), and it adds a certain movement of stretching forward to the beloved. Therefore hope is greater than charity.
Objection 3. Further, a cause is more noble than its effect. Now faith and hope are the cause of charity: for a gloss on Matthew 1:3 says that "faith begets hope, and hope charity." Therefore faith and hope are greater than charity.
On the contrary, The Apostle says (1 Corinthians 13:13): "Now there remain faith, hope, charity, these three; but the greatest of these is charity."
I answer that, As stated above (Article 3), the greatness of a virtue, as to its species, is taken from its object. Now, since the three theological virtues look at God as their proper object, it cannot be said that any one of them is greater than another by reason of its having a greater object, but only from the fact that it approaches nearer than another to that object; and in this way charity is greater than the others. Because the others, in their very nature, imply a certain distance from the object: since faith is of what is not seen, and hope is of what is not possessed. But the love of charity is of that which is already possessed: since the beloved is, in a manner, in the lover, and, again, the lover is drawn by desire to union with the beloved; hence it is written (1 John 4:16): "He that abideth in charity, abideth in God, and God in him."
Reply to Objection 1. Faith and hope are not related to charity in the same way as prudence to moral virtue; and for two reasons. First, because the theological virtues have an object surpassing the human soul: whereas prudence and the moral virtues are about things beneath man. Now in things that are above man, to love them is more excellent than to know them. Because knowledge is perfected by the known being in the knower: whereas love is perfected by the lover being drawn to the beloved. Now that which is above man is more excellent in itself than in man: since a thing is contained according to the mode of the container. But it is the other way about in things beneath man. Secondly, because prudence moderates the appetitive movements pertaining to the moral virtues, whereas faith does not moderate the appetitive movement tending to God, which movement belongs to the theological virtues: it only shows the object. And this appetitive movement towards its object surpasses human knowledge, according to Ephesians 3:19: "The charity of Christ which surpasseth all knowledge."
Reply to Objection 2. Hope presupposes love of that which a man hopes to obtain; and such love is love of concupiscence, whereby he who desires good, loves himself rather than something else. On the other hand, charity implies love of friendship, to which we are led by hope, as stated above (Question 62, Article 4).
Reply to Objection 3. An efficient cause is more noble than its effect: but not a disposing cause. For otherwise the heat of fire would be more noble than the soul, to which the heat disposes the matter. It is in this way that faith begets hope, and hope charity: in the sense, to wit, that one is a disposition to the other.
Source: Summa Theologica (New Advent)