Whether charity is a type of friendship? (II-II q. 23, a. 1, resp.)
According to the Philosopher (Ethic. viii, 2,3) not every love has the character of friendship, but that love which is together with benevolence, when, to wit, we love someone so as to wish good to him. If, however, we do not wish good to what we love, but wish its good for ourselves, (thus we are said to love wine, or a horse, or the like), it is love not of friendship, but of a kind of concupiscence. For it would be absurd to speak of having friendship for wine or for a horse.
Yet neither does well-wishing suffice for friendship, for a certain mutual love is requisite, since friendship is between friend and friend: and this well-wishing is founded on some kind of communication.
Accordingly, since there is a communication between man and God, inasmuch as He communicates His happiness to us, some kind of friendship must needs be based on this same communication, of which it is written (1 Corinthians 1:9): “God is faithful: by Whom you are called unto the fellowship of His Son.” The love which is based on this communication, is charity: wherefore it is evident that charity is the friendship of man for God.