Albert Barnes on Matthew 5:47

And if ye salute your brethren, etc. The word salute here means to show the customary tokens of civility, or to treat with the common marks of friendship. Lk 10:4. He says that the worst men, the very publicans, would do this. Christians should do more; they should show that they had a different spirit; they should treat their enemies as well as wicked men did their friends. This should be done,

(1.) because it is right; it is the only really amiable spirit; and,

(2.) we should show that religion is not selfish, and is superior to all other principles of action.