19 Now I tell you before it come, that, when it is come to pass, ye may believe that I am he.
[AD 253] Origen of Alexandria on John 13:19
And understand the words “that you may believe” as capable of being equivalent to the words “that you may be increased in faith,” while you continue to believe.

[AD 407] John Chrysostom on John 13:12-20
(Hom. lxxi. 1) He speaks now not to Peter alone, but to all: Ye call Me Master and Lord. He accepts their judgment; and to prevent the words being set down merely to favour on their parts, adds, And ye say well, for so I am.

(Hom. lxx. 1) He shows us the greater, that we may do the less. For He was the Lord, but we, if we do it, do it to our fellow-servants: For I have given you an example, that ye should do as I have done to you.

(Hom. lxxi. 2) He continues to urge them to wash one another's feet; Verily, verily, I say unto you, The servant is not greater than his lord, neither He that is sent greater than He that sent Him; as if to say, If I do it, much more ought you.

(Hom. Lxxi. 2) For all know, but all do not do. He then rebukes the traitor, not openly, but covertly: I speak not of you all.

(Hom. lxxi. 1) Then, that He might not sadden them all, He adds, But that the Scripture must be fulfilled, He that eateth bread with Me, hath lifted up his heel against Me: showing that He knew who the traitor was, an intimation that would surely have checked him, if any thing would. He does not say, shall betray Me, but, shall lift up his heel against Me, alluding to his deceit and secret plotting.

(Hom. lxxi. 2) He that eateth bread with Me; i. e. who was fed by Me, who partook of My table. So that if injured ever by our servants or inferiors, we need not be offended. Judas had received infinite benefits, and yet thus requited his Benefactor.

(Hom. Lxxii. 3) As the disciples were about to go forth and to suffer many things, He consoles them by promising His own assistance and that of others; His own, when He says, Happy are ye if ye do them; that of others, in what follows, Verily, verily, I say unto you, He that receiveth whomsoever I send, receiveth Me; and he that receiveth Me receiveth Him that sent Me.

[AD 407] John Chrysostom on John 13:12-20
Now when He had washed their feet, and taken His garments, and sat down, He said, "Know ye what I have done unto you?" He no longer addresseth Himself to Peter only, but to them all.

"Ye call Me Lord and Master, and ye say well, for so I am."

"Ye call Me." He taketh to Him their judgment, and then that the words may not be thought to be words of their kindness, He addeth, "for so I am." By introducing a saying of theirs, He maketh it not offensive, and by confirming it Himself when introduced from them, unsuspected. "For so I am," He saith. Seest thou how when He converseth with the disciples, He speaketh revealing more what belongeth unto Himself?

[AD 407] John Chrysostom on John 13:12-20
"If I then," He saith, "your Lord and Master have washed your feet, ye ought also to wash one another's feet. For I have given you an example, that ye should do as I have done to you."

And yet it is not the same thing, for He is Lord and Master, but ye are fellow-servants one of another. What meaneth then the "as"? "With the same zeal." For on this account He taketh instances from greater actions that we may, if so be, perform the less. Thus schoolmasters write the letters for children very beautifully, that they may come to imitate them though but in an inferior manner. Where now are they who spit on their fellow-servants? where now they who demand honors? Christ washed the feet of the traitor, the sacrilegious, the thief, and that close to the time of the betrayal, and incurable as he was, made him a partaker of His table; and art thou highminded, and dost thou draw up thine eyebrows?

[AD 407] John Chrysostom on John 13:12-20
"Let us then wash one another's feet," saith some one, "then we must wash those of our domestics." And what great thing if we do wash even those of our domestics? In our case "slave" and "free" is a difference of words; but there an actual reality. For by nature He was Lord and we servants, yet even this He refused not at this time to do. But now it is matter for contentment if we do not treat free men as bondmen, as slaves bought with money. And what shall we say in that day, if after receiving proofs of such forbearance, we ourselves do not imitate them at all, but take the contrary part, being in diametrical opposition, lifted up, and not discharging the debt? For God hath made us debtors one to another, having first so done Himself, and hath made us debtors of a less amount. For He was our Lord, but we do it, if we do it at all, to our fellow-servants, a thing which He Himself implied by saying, "If I then your Lord and Master-so also do ye." It would indeed naturally have followed to say, "How much more should ye servants," but He left this to the conscience of the hearers.

[AD 407] John Chrysostom on John 13:12-20
But why hath He done this "now"? They were for the future to enjoy, some greater, some less honor. In order then that they may not exalt themselves one above the other, and say as they did before, "Who is the greatest," nor be angry one against the other, He taketh down the high thoughts of them all, by saying, that "although thou mayest be very great, thou oughtest to have no high thoughts towards thy brother." And He mentioned not the greater action, that "if I have washed the feet of the traitor, what great matter if ye one another's?" but having exemplified this by deeds, He then left it to the judgment of the spectators.

[AD 407] John Chrysostom on John 13:12-20
"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 ye know these things, happy are ye if ye do them. I speak not of you all - but that the Scripture may be fulfilled, He that eateth bread with Me hath lifted up his heel against Me."

What He said before, this He saith 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 sayest Thou these things? Do we not already know them?" He addeth 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," belongeth to all; but "to do," not to all. On this account He said, "Blessed are ye if ye 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.

[AD 407] John Chrysostom on John 13:12-20
"I speak not," He saith, "of you all." O what forbearance! Not yet doth He convict the traitor, but veileth the matter, hence giving him room for repentance. He convicteth and yet doth not convict him when He saith thus, "He that eateth bread with Me hath 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 eateth bread with Me," and letting pass all the rest, He hath put that which was most fitted to restrain and shame him; "he who was fed by Me," He saith, "and who shared My table." And He spake the words, to instruct them to benefit those who did evil to them, even though such persons should continue incurable.

[AD 407] John Chrysostom on John 13:12-20
But having said, "I speak not of you all," in order not to attach fear to more than one, He at last separateth the traitor, speaking thus; "He that eateth bread with Me." For the, "not of you all," doth not direct the words to any single one, therefore He added, "He that eateth 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, "betrayeth Me," but, "hath lifted up his heel against Me," desiring to represent the deceit, the treachery, the secrecy of the plot.

[AD 428] Theodore of Mopsuestia on John 13:19
I could not reveal what was about to happen, he says. However, in order that you might not think that I did not know the thoughts of those who follow me—or that I was unaware of what was happening to me and therefore striving in vain because of the shameful things that were happening to me—I foretell the facts before the event so that when they happen you will know who I am.

[AD 430] Augustine of Hippo on John 13:19
"From this time," Christ adds, "I tell you before it come; that when it is come to pass, ye may believe that I am He:" that is, I am He of whom the Scripture that preceded has just said, "He that eateth bread with me, shall lift up his heel upon me."

[AD 430] Augustine of Hippo on John 13:19
Now I tell you before it come, that when it is come, ye may believe that I am He, i. e. of whom that Scripture foretold.

[AD 444] Cyril of Alexandria on John 13:19
I have been led on, He says, by very urgent reasons to give you, even before the time, this account of the events that will very shortly happen. For it will gratify those who hear Me, and bring them no slight advantage, if they know My aim in the matter. For to be recklessly wasteful in the use of words in meaningless dissertations is contrary to My custom and pleasure: but whatsoever seems likely to be fraught with no slight profit to you provided you have knowledge of it, this I feel constrained to instil in your ears. From henceforth therefore, He says, I tell you things that are even now at the doors, and I implant in you the knowledge of things not yet fulfilled; that, when the time for their occurrence has come, you may be able to harmonise the final issue of the matters with the prophecies uttered by Me, and so may believe that I am He concerning Whom the Divine Scripture has uttered such oracles. At one and the same time therefore our Lord Jesus the Christ wisely attempts to correct the traitor, putting forward His rebuke in a form concealed under slight obscurities, as well as to show that the issue of the treachery would be a sure sign and most clear indication of the fact that He is Christ. For, as we have already said by anticipation, any one who compared the utterances recorded from old time in the sacred Scriptures with the daring deeds of the traitor, would perceive I think very clearly and without difficulty that their interpretation in reference to Him was certainly and very evidently true.