What reward have ye? - The word “reward” seems to be used in the sense of “deserving of praise.” If you only love those that love you, you are selfish; it is not genuine love for the “character,” but love for the “benefit,” and you deserve no commendation. The very “publicans” would do the same.
The publicans - The publicans were tax-gatherers. Judea was a province of the Roman empire. The Jews bore this foreign yoke with great impatience, and paid their taxes with great reluctance. It happened, therefore, that those who were appointed to collect taxes were objects of great detestation. They were, besides, people who would be supposed to execute their office at all hazards; men who were willing to engage in an odious and hated employment; people often of abandoned character, oppressive in their exactions, and dissolute in their lives. By the Jews they were associated in character with thieves and adulterers; with the profane and the dissolute. Christ says that even these wretched people would love their benefactors.