On friendship

“CONSEQUENTLY youths, who find much pleasure in conversation and readily agree with others, quickly make friends. This does not happen with old people, for they cannot become friends of those whose company and conversation they do not enjoy. The same reason holds for morose persons who are quarrelsome and critical of what others do. But such people, i.e., the elderly and the severe, can be benevolent inasmuch as they affectively wish good to others and even effectively assist them in their needs. However, they do not really become friends because they do not live with nor take pleasure in the company of their friends—activities that seem to be the special works of friendship.”

~St. Thomas Aquinas: Commentary on Aristotle’s Nicomachean Ethics, Book 8, Lect. VI

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Charity and friendship

"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. . . it is love not of friendship, but of a kind of concupiscence. . . . 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."

~St. Thomas Aquinas: Summa Theologica, II-II, Q. 23, A. 1.

Read more: Charity, considered in itself

"Charity is friendship"

"IT IS written (Jn 15:15): "I will not now call you servants . . . but My friends." Now this was said to them by reason of nothing else than charity. Therefore charity is friendship.

"... 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, how...ever, 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 Cor 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."

~St. Thomas Aquinas: S.T. II-II q. 23, a. 1.