Jamieson, Fausset and Brown on Matthew 5:11

11. Blessed are ye when men shall revile you--or abuse you to your face, in opposition to backbiting. (See Mr 15:32).

and persecute you, and shall say all manner of evil against you, falsely, for my sake--Observe this. He had before said, "for righteousness' sake." Here He identifies Himself and His cause with that of righteousness, binding up the cause of righteousness in the world with the reception of Himself. Would Moses, or David, or Isaiah, or Paul have so expressed themselves? Never. Doubtless they suffered for righteousness' sake. But to have called this "their sake," would, as every one feels, have been very unbecoming. Whereas He that speaks, being Righteousness incarnate (see Mr 1:24; Ac 3:14; Re 3:7), when He so speaks, speaks only like Himself.