John 13:16-18
“Verily I say unto you, the servant is not greater than his lord, neither he that is sent greater than he that sent him. If you know these things, happy are you if you do them. I speak not of you all —but that the Scripture may be fulfilled, He that eats bread with Me has lifted up his heel against Me.”
What He said before, this He says here also, to shame them; “For if the servant is not greater than his master, nor he that is sent greater than him that sent him, and these things have been done by Me, much more ought they to be done by you.” Then, lest any one should say, “Why now do You say these things? Do we not already know them?” He adds this very thing, “I speak not to you as not knowing, but that by your actions ye may show forth the things spoken of.” For “to know,” belongs to all; but “to do,” not to all. On this account He said, “Blessed are you if you do them”; and on this account I continually and ever say the same to you, although ye know it, that I may set you on the work. Since even Jews “know,” but yet they are not “blessed”; for they do not what they know.
“I speak not,” He says, “of you all.” O what forbearance! Not yet does He convict the traitor, but veils the matter, hence giving him room for repentance. He convicts and yet does not convict him when He says thus, “He that eats bread with Me has lifted up his heel against Me.” It seems to me that the, “The servant is not greater than his lord,” was uttered for this purpose also, that if any persons should at any time suffer harm either from domestics or from any of the meaner sort, they should not be offended; looking to the instance of Judas, who having enjoyed ten thousand good things, repaid his Benefactor with the contrary. On this account He added, “He that eats bread with Me,” and letting pass all the rest, He has put that which was most fitted to restrain and shame him; “he who was fed by Me,” He says, “and who shared My table.” And He spoke the words, to instruct them to benefit those who did evil to them, even though such persons should continue incurable.
But having said, “I speak not of you all,” in order not to attach fear to more than one, He at last separates the traitor, speaking thus; “He that eats bread with Me.” For the, “not of you all,” does not direct the words to any single one, therefore He added, “He that eats bread with Me”; showing to that wretched one that He was not seized in ignorance, but even with full knowledge; a thing which of itself was most of all fitted to restrain him. And He said not, “betrays Me,” but, “has lifted up his heel against Me,” desiring to represent the deceit, the treachery, the secrecy of the plot.
3. These things are written that we bear not malice towards those who injure us; but rebuke them and weep for them; for the fit subjects of weeping are not they who suffer, but they who do the wrong. The grasping man, the false accuser, and whoso works any other evil thing, do themselves the greatest injury, and us the greatest good, if we do not avenge ourselves. Such a case as this: some one has robbed you; have you given thanks for the injury, and glorified God? By that thanksgiving you have gained ten thousand rewards, just as he has gathered for himself fire unspeakable. But if any one say, “How then, if I 'could' not defend myself against him who wronged me, being weaker?” I would say this, that you could have put into action the being discontented, the being impatient, (for these things are in our power,) the praying against him, who grieved you, the uttering ten thousand curses against him, the speaking ill of him to every one. He therefore who has not done these things shall even be rewarded for not defending himself, since it is clear that even if he had had the power, he would not have done it. The injured man uses any weapon that comes to hand, when, being little of soul, he defends himself against one who has injured him, by curses, by abuse, by plotting. Do thou then not only not do these things, but even pray for him; for if you do them not, but wilt even pray for him, you have become like God. For, “pray,” it says, “for them, that despitefully use you— that you may be like your Father which is in Heaven.” Do you see how we are the greatest gainers from the insolence of others? Nothing so delights God, as the not returning evil for evil? But what say I? Not returning evil for evil? Surely we are enjoined to return the opposite, benefits, prayers. Wherefore Christ also repaid him who was about to betray Him with everything opposite. He washed his feet, convicted him secretly, rebuked him sparingly, tended him, allowed him to share His table and His kiss, and not even by these was he made better; nevertheless (Christ) continued doing His own part.
Source: Homilies on the Gospel of John (New Advent)