Objection 1. It would seem that charity need not be loved out of charity. For the things to be loved out of charity are contained in the two precepts of charity (Matthew 22:37-39): and neither of them includes charity, since charity is neither God nor our neighbor. Therefore charity need not be loved out of charity.
Objection 2. Further, charity is founded on the fellowship of happiness, as stated above (Question 23, Article 1). But charity cannot participate in happiness. Therefore charity need not be loved out of charity.
Objection 3. Further, charity is a kind of friendship, as stated above (Question 23, Article 1). But no man can have friendship for charity or for an accident, since such things cannot return love for love, which is essential to friendship, as stated in Ethic. viii. Therefore charity need not be loved out of charity.
On the contrary, Augustine says (De Trin. viii, 8): "He that loves his neighbor, must, in consequence, love love itself." But we love our neighbor out of charity. Therefore it follows that charity also is loved out of charity.
I answer that, Charity is love. Now love, by reason of the nature of the power whose act it is, is capable of reflecting on itself; for since the object of the will is the universal good, whatever has the aspect of good, can be the object of an act of the will: and since to will is itself a good, man can will himself to will. Even so the intellect, whose object is the true, understands that it understands, because this again is something true. Love, however, even by reason of its own species, is capable of reflecting on itself, because it is a spontaneous movement of the lover towards the beloved, wherefore from the moment a man loves, he loves himself to love.
Yet charity is not love simply, but has the nature of friendship, as stated above (Question 23, Article 1). Now by friendship a thing is loved in two ways: first, as the friend for whom we have friendship, and to whom we wish good things: secondly, as the good which we wish to a friend. It is in the latter and not in the former way that charity is loved out of charity, because charity is the good which we desire for all those whom we love out of charity. The same applies to happiness, and to the other virtues.
Reply to Objection 1. God and our neighbor are those with whom we are friends, but love of them includes the loving of charity, since we love both God and our neighbor, in so far as we love ourselves and our neighbor to love God, and this is to love charity.
Reply to Objection 2. Charity is itself the fellowship of the spiritual life, whereby we arrive at happiness: hence it is loved as the good which we desire for all whom we love out of charity.
Reply to Objection 3. This argument considers friendship as referred to those with whom we are friends.
Source: Summa Theologica (New Advent)