36 Simon Peter said unto him, Lord, whither goest thou? Jesus answered him, Whither I go, thou canst not follow me now; but thou shalt follow me afterwards.
[AD 253] Origen of Alexandria on John 13:36
The Word, however, departs on his own courses, and he who follows the Word follows him. But one who is not prepared to walk in his steps persistently cannot follow, since the Word leads those to his Father who do all things that they might be able to follow him and that they may follow him until they may say to the Christ, “My soul has clung to you.”

[AD 397] Ambrose of Milan on John 13:36
Therefore, he prudently asks to be drawn, because not everyone can follow. Finally, when Peter said, "Where are you going?" the Word of God answered, "You cannot follow me now, but you will follow later" (John 13:36). He entrusted the keys of the kingdom of heaven to her and considered her equal by following him. However, he did not delay this soul; because she did not presume, but she asked.

[AD 407] John Chrysostom on John 13:36-38
(Hom. lxxiii. 3) Great is love, and stronger than fire; nothing can stop its course. Peter the most ardent of all, as soon as he hears our Lord say, Whither I go ye cannot follow Me now, asks, Lord, whither goest Thou?

(Hom. lxxii. 1) Peter, on receiving this answer, does not check his desire, but hastily conceives favourable hopes from it, and having got rid of the fear of betraying our Lord, feels secure, and becomes himself the interrogator, while the rest are silent: Peter said unto Him, Lord, why cannot I follow Thee now? I will lay down my life for Thy sake. What sayest thou, Peter? He hath said, thou canst not, and thou sayest, thou canst: wherefore thou shalt know by experience, that thy love is nothing, unless thou art enabled from above: Jesus answered him, Will thou lay down thy life for My sake?

(Hom. lxxiii. 1) It is manifest that our Lord permitted Peter's fall. He might have recalled him to begin with, but as he persisted in his vehemence, though He did not drive him to a denial, He let him go without assistance, that He might learn his own weakness, and not fall into such sin again, when the superintendence of the world had come to him, but that remembering what had happened to himd, he might know himself.

[AD 407] John Chrysostom on John 13:36-38
A great thing is love, and stronger than fire itself, and it goeth up to the very heaven; there is no hindrance which can restrain its tearing force. And so the most fervent Peter, when he hears, "Whither I go ye cannot come," what saith he? "Lord, whither goest thou?" and this he said, not so much from wish to learn, as from desire to follow. To say openly, "I go," he dared not yet, but, "Whither goest thou?" Christ answered, not to his words, but to his thoughts. For that this was his wish, is clear from what Christ said, "Whither I go thou canst not follow Me now." Seest thou that he longed for the following Him, and therefore asked the question? And when he heard, "thou shalt follow Me afterwards" not even so did he restrain his longing, and, though he had gained good hopes, he is so eager as to say, "Why cannot I follow Thee now? I will lay down my life for Thee."

[AD 407] John Chrysostom on John 13:36-38
When he had shaken off the dread of being the traitor, and was shown to be one of His own, he afterwards asked boldly himself, while the others held their peace. "What sayest thou, Peter? He said, 'thou canst not,' and thou sayest, 'I can'? Therefore thou shalt know from this temptation that thy love is nothing without the presence of the impulse from above." Whence it is clear that in care for him He allowed even that fall. He desired indeed to teach him even by the first words, but when he continued in his vehemence, He did not indeed throw or force him into the denial, but left him alone, that he might learn his own weakness.

[AD 407] John Chrysostom on John 13:36-38
Christ had said that He must be betrayed; Peter replied, "Be it far from Thee, Lord; this shall not happen unto Thee." He was rebuked, but not instructed. On the contrary, when Christ desired to wash his feet, he said, "Thou shall never wash my feet." Again, when he hears, "Thou canst not follow Me now," he saith, "Though all deny Thee, I will not deny Thee." Since then it was likely that he would be lifted up to folly by his practice of contradiction, Jesus next teacheth him not to oppose Him. This too Luke implies, when he telleth us that Christ said, "And I have prayed for thee, that thy faith fail not"; that is, "that thou be not finally lost." In every way teaching him humility, and proving that human nature by itself is nothing.

[AD 407] John Chrysostom on John 13:36-38
But, since great love made him apt for contradiction, He now sobereth him, that he might not in after times be subject to this, when he should have received the stewardship of the world, but remembering what he had suffered, might know himself. And look at the violence of his fall; it did not happen to him once or twice, but he was so beside himself, that in a short time thrice did he utter the words of denial, that he might learn that he did not so love as he was loved. And yet, to one who had so fallen He saith again, "Lovest thou Me more than these?" So that the denial was caused not by the cooling of his love, but from his having been stripped of aid from above. He accepteth then Peter's love, but cutteth off the spirit of contradiction engendered by it. "For if thou lovest, thou oughtest to obey Him who is beloved."

[AD 407] John Chrysostom on John 13:36-38
"I will lay down my life for Thee." For since he had heard, "Greater love than this hath no man," he straightway sprang forward, insatiably eager and desirous to reach even to the highest pitch of virtue. But Christ, to show that it belonged to Himself alone to promise these things with authority, saith, "Before the cock crow." That is, "now"; there was but a little interval. He spake when it was late at night, and the first and second watch was past.

[AD 430] Augustine of Hippo on John 13:36
(Tr. lxvi. 1) The disciple asks this, as if he were ready to follow. But our Lord saw his heart; Jesus answered him, Whither I go, thou canst not follow Me now; He checks his forwardness, but does not destroy his hope; nay, confirms it; But thou shalt follow Me afterwards. Why hastenest thou, Peter? The Rock has not yet established thee with His spirit. Be not lifted up with presumptions, thou canst not now; be not cast down with despair, thou shalt follow Me afterwards.

[AD 430] Augustine of Hippo on John 13:36
While the Lord Jesus was commending to the disciples that holy love wherewith they should love one another, "Simon Peter saith unto Him, Lord, whither goest Thou?" So, at all events, said the disciple to his Master, the servant to his Lord, as one who was prepared to follow. Just as for the same reason the Lord, who read in his mind the purpose of such a question, made him this reply: "Whither I go, thou canst not follow me now;" as if He said, In reference to the object of thy asking, thou canst not now. He does not say, Thou canst not; but "Thou canst not now." He intimated delay, without depriving of hope; and that same hope, which He took not away, but rather bestowed, in His next words He confirmed, by proceeding to say, "Thou shall follow me afterwards." Why such haste, Peter? The Rock (petra) has not yet solidified thee by His Spirit. Be not lifted up with presumption, "Thou canst not now;" be not cast now into despair, "Thou shalt follow afterwards."

[AD 444] Cyril of Alexandria on John 13:36
Simon Peter saith unto Him, Lord, whither goest Thou?

Peter again with his usual curiosity is anxious to learn more, and busies himself about the significance of Christ's words, not yet (as seems probable) comprehending the real meaning of what had been said, yet feeling with all the force of his fiery zeal that it was his duty to follow Christ. And in this matter most admirable is the behaviour of the disciples. For certainly no one would allow that it was only the chief disciple who was in ignorance while the others fully understood the matter, and that this was why he asked the question. I should rather say that they yielded to him, as chief among them, the privilege of speaking first, and of taking the initiative in courageous inquiry. For the speaking into the ears of their Master was no light and easy matter, even for those who were reputed to be somewhat. And the conduct of Peter is no less admirable, who is harassed by no fear of being thought sluggish in the comprehension of those matters of which he was ignorant, but zealously seeks for enlightenment, considering that the profit he will derive from gratifying his love of knowledge will be of more value than an unseasonable sense of shame: and so in this also he is a pattern to those that live after him. For we ought never, I think, to pass over the words of our teachers, even though they may not be so very distinct, merely for the sake of seeming to be shrewd people and very quick in intelligence; but rather to investigate the meaning and search it out wisely, in the teaching at first delivered to us for our profit. For the knowledge of what is useful is far nobler than a vain semblance of wisdom, and far better is it to learn a thing in reality than merely to seem to know all about it.

[AD 444] Cyril of Alexandria on John 13:36
The disciples had not yet been clothed with the power from on high, neither had they received the strength that was to invigorate them and impart courage to their character—I mean the gift of the Holy Spirit. Thus, they were not able to wrestle with death and engage in a conflict with terrors so hard to face.