18 Verily, verily, I say to thee, When thou wast young, thou girdedst thyself, and walkedst where thou desiredst; but when thou shalt be old, thou shalt stretch forth thy hands, and another shall gird thee, and bring thee where thou dost not desire. 19 But he said this signifying by what death he should glorify God. And having said this, he says to him, Follow me.
20 Peter, turning round, sees the disciple whom Jesus loved following, who also leaned at supper on his breast, and said, Lord, who is it that delivers thee up? 21 Peter, seeing him, says to Jesus, Lord, and what [of] this [man]? 22 Jesus says to him, If I will that he abide until I come, what [is that] to thee? Follow thou me.
Matthew Henry's Commentary on John 21:18-22
Commentary on John 21:15-19
(Read John 21:15-19)
Our Lord addressed Peter by his original name, as if he had forfeited that of Peter through his denying him. He now answered, Thou knowest that I love thee; but without professing to love Jesus more than others. We must not be surprised to have our sincerity called into question, when we ourselves have done that which makes it doubtful. Every remembrance of past sins, even pardoned sins, renews the sorrow of a true penitent. Conscious of integrity, Peter solemnly appealed to Christ, as knowing all things, even the secrets of his heart. It is well when our falls and mistakes make us more humble and watchful. The sincerity of our love to God must be brought to the test; and it behoves us to inquire with earnest, preserving prayer to the heart-searching God, to examine and prove us, whether we are able to stand this test. No one can be qualified to feed the sheep and lambs of Christ, who does not love the good Shepherd more than any earthly advantage or object. It is the great concern of every good man, whatever death he dies, to glorify God in it; for what is our chief end but this, to die to the Lord, at the word of the Lord?
Commentary on John 21:20-24
(Read John 21:20-24)
Sufferings, pains, and death, will appear formidable even to the experienced Christian; but in the hope to glorify God, to leave a sinful world, and to be present with his Lord, he becomes ready to obey the Redeemer's call, and to follow Him through death to glory. It is the will of Christ that his disciples should mind their own duty, and not be curious about future events, either as to themselves or others. Many things we are apt to be anxious about, which are nothing to us. Other people's affairs are nothing to us, to intermeddle in; we must quietly work, and mind our own business. Many curious questions are put about the counsels of God, and the state of the unseen world, as to which we may say, What is this to us? And if we attend to the duty of following Christ, we shall find neither heart nor time to meddle with that which does not belong to us. How little are any unwritten traditions to be relied upon! Let the Scripture be its own interpreter, and explain itself; as it is, in a great measure, its own evidence, and proves itself, for it is light. See the easy setting right such mistakes by the word of Christ. Scripture language is the safest channel for Scripture truth; the words which the Holy Ghost teaches, 1 Corinthians 2:13. Those who cannot agree in the same terms of art, and the application of them, may yet agree in the same Scripture terms, and to love one another.