Today's section of St John's Gospel continues on from the story of the miraculous catch of fish, and includes the important 'commissioning' of St Peter.
The New Advent page can be found here.
2 Dicit eis Jesus: Venite, prandete. Et nemo audebat discumbentium interrogare eum: Tu quis es? scientes, quia Dominus est. 13 Et venit Jesus, et accipit panem, et dat eis, et piscem similiter. 14 Hoc jam tertio manifestatus est Jesus discipulis suis cum resurrexisset a mortuis.15 Cum ergo prandissent, dicit Simoni Petro Jesus: Simon Joannis, diligis me plus his? Dicit ei: Etiam Domine, tu scis quia amo te. Dicit ei: Pasce agnos meos. 16 Dicit ei iterum: Simon Joannis, diligis me? Ait illi: Etiam Domine, tu scis quia amo te. Dicit ei: Pasce agnos meos. 17 Dicit ei tertio: Simon Joannis, amas me? Contristatus est Petrus, quia dixit ei tertio: Amas me? et dixit ei: Domine, tu omnia nosti, tu scis quia amo te. Dixit ei: Pasce oves meas. 18 Amen, amen dico tibi: cum esses junior, cingebas te, et ambulabas ubi volebas: cum autem senueris, extendes manus tuas, et alius te cinget, et ducet quo tu non vis. 19 Hoc autem dixit significans qua morte clarificaturus esset Deum. Et cum hoc dixisset, dicit ei: Sequere me.
From the Douay-Rheims:
 Jesus saith to them: Come, and dine. And none of them who were at meat, durst ask him: Who art thou? knowing that it was the Lord.  And Jesus cometh and taketh bread, and giveth them, and fish in like manner.  This is now the third time that Jesus was manifested to his disciples, after he was risen from the dead.  When therefore they had dined, Jesus saith to Simon Peter: Simon son of John, lovest thou me more than these? He saith to him: Yea, Lord, thou knowest that I love thee. He saith to him: Feed my lambs. He saith to him again: Simon, son of John, lovest thou me? He saith to him: Yea, Lord, thou knowest that I love thee. He saith to him: Feed my lambs.  He said to him the third time: Simon, son of John, lovest thou me? Peter was grieved, because he had said to him the third time: Lovest thou me? And he said to him: Lord, thou knowest all things: thou knowest that I love thee. He said to him: Feed my sheep.  Amen, amen I say to thee, when thou wast younger, thou didst gird thyself, and didst walk where thou wouldst. But when thou shalt be old, thou shalt stretch forth thy hands, and another shall gird thee, and lead thee whither thou wouldst not.  And this he said, signifying by what death he should glorify God. And when he had said this, he saith to him: Follow me.
The Catena Aurea anthology on the reasons for Jesus' questioning of Peter:
THEOPHYL. The dinner being ended, He commits to Peter the superintendence over the sheep of the world, not to the others: So when they had dined, Jesus says to Simon Peter, Simon, son of Jonas, Do love you Me more than these do?
AUG. Our Lord asked this, knowing it: He knew that Peter not only loved Him, but loved Him more than all the rest.
ALCUIN. He is called Simon, son of John, John being his natural father. But mystically, Simon is obedience, John grace, a name well befitting him who was so obedient to God's grace, that he loved our Lord more ardently than any of the others. Such virtue arising from divine gift, not mere human will.
AUG. While our Lord was being condemned to death, he feared, and denied Him. But by His resurrection Christ implanted love in his heart, and drove away fear. Peter denied, because he feared to die: but when our Lord was risen from the dead, and by His death destroyed death, what should he fear? He says to Him, Yea, Lord; you know that 1 love You. On this confession of his love, our Lord commends His sheep to him: He says to him, Feed My lambs. as if there were no way of Peter's showing his love for Him, but by being a faithful shepherd, under the chief Shepherd.
CHRYS. That which most of all attracts the Divine love is care and love for our neighbor. Our Lord passing by the rest, addresses this command to Peter: he being the chief of the Apostles, the mouth of the disciples, and head of the college. Our Lord remembers no more his sin in denying Him, or brings that as a charge against him, but commits to him at once the superintendence over his brethren. If you love Me, have rule over your brethren, show forth that love which you have evidenced throughout, and that life which you said you would lay down for Me, lay down for the sheep.
He says to him again the second time, Simon, son of Jonas, love you Me? He says to Him, Yea, Lord; you know that I love You. Well does He say to Peter, Love you Me, and Peter answer, Amo Te, and our Lord replies again, Feed My lambs. Whereby, it appears that amor and dilectio are the same thing: especially as our Lord the third time He speaks does not say, Diligis Me, but Amas Me.
He says to him the third time, Simon, son of Jonas, love you Me? A third time our Lord asks Peter whether he loves Him. Three confessions are made to answer to the three denials; that the tongue might show as much love as it had fear, and life gained draw out the voice as much as death threatened.
CHRYS. A third time He asks the same question, and gives the same command; to show of what importance He esteems the superintendence of His own sheep, and how He regards it as the greatest proof of love to Him.
THEOPHYL. Thence is taken the custom of threefold confession in baptism.
CHRYS. The question asked for the third time disturbed him: Peter was grieved because He said to him the third time, Love you Me? He was afraid perhaps of receiving a reproof again for professing to love more than he did. So he appeals to Christ Himself: And he said to Him, Lord, you know all things, i.e. the secrets of the heart, present and to come.
AUG. He was grieved because he was asked so often by Him Who knew what He asked, and gave the answer. He replies therefore from his inmost heart; you know that I love You.
AUG. He says no more, He only replies what he knew himself; he knew he loved Him; whether any else loved Him he could not tell, as he could not see into another's heart: Jesus says to him, Feed My sheep; as if to say, Be it the office of love to feed the Lord's flock, as it was the resolution of fear to deny the Shepherd.
The nature of the commission:
THEOPHYL. There is a difference perhaps between lambs and sheep. The lambs are those just initiated, the sheep are the perfected.
ALCUIN. To feed the sheep is to support the believers in Christ from falling from the faith, to provide earthly sustenance for those under us, to preach and exemplify withal our preaching by our lives, to resist adversaries, to correct wanderers.
AUG. They who feed Christ's sheep, as if they were their own, not Christ's, show plainly that they love themselves, not Christ; that they are moved by lust of glory, power, gain, not by the love of obeying, ministering, pleasing God. Let us love therefore, not ourselves, but Him, and in feeding His sheep, seek not our own, but the things which are His. For whoso loves himself, not God, loves not himself: man that cannot live of himself, must die by loving himself; and he cannot love himself, who loves himself to his own destruction. Whereas when He by Whom we live is loved, we love ourselves the more, because we do not love ourselves; because we do not love ourselves in order that we may love Him by Whom we live
AUG. But unfaithful servants arose, who divided Christ's flock, and handed down the division to their successors: and you hear them say, Those sheep are mine, what seek you with my sheep, I will not let you come to my sheep. If we call our sheep ours, as they call them theirs, Christ has lost His sheep.
On St Peter's future martyrdom:
CHRYS. Our Lord having made Peter declare his love, informs him of his future martyrdom; an intimation to us how we should love: Verily, verily, I say to you, When you were young, you girded yourself, and walked where you would. He reminds him of his former life, because, whereas in worldly matters a young man has powers, an old man none; in spiritual things, on the contrary, virtue is brighter, manliness stronger, in old age; age is no hindrance to grace. Peter had all along desired to share Christ's dangers; so Christ tells him, Be of good cheer; I will fulfill your desire in such a way, that what you has not suffered when young, you shall suffer when old: But when you are old. Whence it appears, that he was then neither a young nor an old man, but in the prime of life.
ORIGEN. It is not easy to find any ready to pass at once from this life; and so he says to Peter, When you are old, you shall stretch forth your hand.
AUG. That is, shall be crucified. And to come to this end, Another shall gird you, and carry you where you would not. First He said what would come to pass, secondly, how it would come to pass. For it was not when crucified, but when about to be crucified, that he was led where he would not. He wished to be released from the body, and be with Christ; but, if it were possible, he wished to attain to eternal life without the pains of death; to which he went against his will, but conquered by the force of his will, and triumphing over the human feeling, so natural a one, that even old age could not deprive Peter of it. But whatever be the pain of death, it ought to be conquered by the strength of love for Him, Who being our life, voluntarily also underwent death for us. For if there is no pain in death, or very little, the glory of martyrdom would not be great.
CHRYS. He says, Where you would not, with reference to the natural reluctance of the soul to be separated from the body; an instinct implanted by God to prevent men putting an end to themselves.
Then raising the subject, the Evangelist says, This spoke He, signifying by what death he should glorify God: not, should die: he expresses himself so, to intimate that to suffer for Christ was the glory of the sufferer. But unless the mind is persuaded that He is very God, the sight of Him can in no way enable us to endure death. Wherefore the death of the saints is certainty of divine glory.
AUG. He who denied and loved, died in perfect love for Him, for Whom he had promised to die with wrong haste. It was necessary that Christ should first die for Peter's salvation, and then Peter die for Christ's Gospel.