Objection 1. It would seem that charity is not a special virtue. For Jerome says: "Let me briefly define all virtue as the charity whereby we love God" [The reference should be to Augustine, Ep. clxvii]: and Augustine says (De Moribus Eccl. xv) [De Civ. Dei xv, 22 that "virtue is the order of love." Now no special virtue is included in the definition of virtue in general. Therefore charity is not a special virtue.
Objection 2. Further, that which extends to all works of virtue, cannot be a special virtue. But charity extends to all works of virtue, according to 1 Corinthians 13:4: "Charity is patient, is kind," etc.; indeed it extends to all human actions, according to 1 Corinthians 16:14: "Let all your things be done in charity." Therefore charity is not a special virtue.
Objection 3. Further, the precepts of the Law refer to acts of virtue. Now Augustine says (De Perfect. Human. Justit. v) that, "Thou shalt love" is "a general commandment," and "Thou shalt not covet," "a general prohibition." Therefore charity is a general virtue.
On the contrary, Nothing general is enumerated together with what is special. But charity is enumerated together with special virtues, viz. hope and faith, according to 1 Corinthians 13:13: "And now there remain faith, hope, charity, these three." Therefore charity is a special virtue.
I answer that, Acts and habits are specified by their objects, as shown above (I-II, 18, 2; I-II, 54, 2). Now the proper object of love is the good, as stated above (I-II, 27, 1), so that wherever there is a special aspect of good, there is a special kind of love. But the Divine good, inasmuch as it is the object of happiness, has a special aspect of good, wherefore the love of charity, which is the love of that good, is a special kind of love. Therefore charity is a special virtue.
Reply to Objection 1. Charity is included in the definition of every virtue, not as being essentially every virtue, but because every virtue depends on it in a way, as we shall state further on (A7,8). On this way prudence is included in the definition of the moral virtues, as explained in Ethic. ii, vi, from the fact that they depend on prudence.
Reply to Objection 2. The virtue or art which is concerned about the last end, commands the virtues or arts which are concerned about other ends which are secondary, thus the military art commands the art of horse-riding (Ethic. i). Accordingly since charity has for its object the last end of human life, viz. everlasting happiness, it follows that it extends to the acts of a man's whole life, by commanding them, not by eliciting immediately all acts of virtue.
Reply to Objection 3. The precept of love is said to be a general command, because all other precepts are reduced thereto as to their end, according to 1 Timothy 1:5: "The end of the commandment is charity."
Source: Summa Theologica (New Advent)