For when we are knit together in parties of two or three, and the two indeed, or three or four, are closely bound to one another, but draw themselves off from the rest, because they can have recourse to these, and in all things confide in these; this is the division of love-- not love. For tell me, if the eye should bestow upon the hand the foresight which it has for the whole body, and withdrawing itself from the other members, should attend to that alone, would it not injure the whole? Assuredly. So also if we confine to one or two the love which ought to be extended to the whole Church of God, we injure both ourselves and them, and the whole. For these things are not of love, but of division; schisms, and distracting rents. Since even if I separate and take a member from the whole man, the part separated indeed is united in itself, is continuous, all compacted together, yet even so it is a separation, since it is not united to the rest of the body.
For what advantage is it, that you love a certain person exceedingly? It is a human love. But if it is not a human love, but you love for God's sake, then love all. For so God has commanded to love even our enemies. And if He has commanded to love our enemies, how much more those who have never aggrieved us? But, do you say, I love, but not in that way. Rather, you do not love at all. For when you accuse, when you envy, when you lay snares, how do you love? But, do you say, I do none of these things. But when a man is ill spoken of, and you do not shut the mouth of the speaker, dost not disbelieve his sayings, dost not check him, of what love is this the sign? And the love, he says, of each one of you all toward one another abounds.
(from Saint John Chrysostom, Homily on 2 Thessalonians 1:1-2)