From: John 13:21-33, 36-38
The Treachery of Judas Foretold
 When Jesus had thus spoken, He was troubled in spirit, and testified, "Truly, truly, I say to you, one of you will betray Me."  The disciples looked at one another, uncertain of whom He spoke.  One of His disciples, whom Jesus loved, was lying close to the breast of Jesus;  so Simon Peter beckoned to Him and said, "Tell us who it is of whom He speaks."  So lying thus, close to the breast of Jesus, he said to Him, "Lord, who is it?"  Jesus answered, "It is he to whom I shall give this morsel when I have dipped it." So when He had dipped the morsel, He gave it to Judas, the son of Simon Iscariot.  Then after the morsel, Satan entered into him. Jesus said to him, "What you are going to do, do quickly."  Now no one at the table knew why He said this to him.  Some thought that, because Judas had the money box, Jesus was telling him, "Buy what you need for the feast"; or, that he should give something to the poor.  So, after receiving the morsel, he immediately went out; and it was night.
 When he had gone out, Jesus said, "Now is the Son of Man glorified, and in Him God is glorified;  if God is glorified in Him, God will also glorify Him in Himself, and glorify Him at once.  Little children, yet a little while I am with you. You will seek Me, and as I said to the Jews so now I say to you, `Where I am going you cannot come.'  Simon Peter said to Him, "Lord, where are You going?" Jesus answered, "Where I am going you cannot follow Me now; but you shall follow Me afterward."  Peter said to Him, "Lord, why cannot I follow You now? I will lay down my life for You."  Jesus answered, "Will you lay down your life for Me? Truly, truly, I say to you, the cock will not crow, till you have denied Me three times."
21. Christ's sadness is proportionate to the gravity of the offense. Judas was one of those whom Jesus chose to be an Apostle: he had been on intimate terms with Him for three years, he had followed Him everywhere, had seen His miracles, had heard His divine teaching, and experienced the tenderness of His affection. And despite all that, when the moment of truth comes, Judas not only abandons the Master but betrays Him and sells Him. Betrayal by an intimate friend is something much more painful and cruel than betrayal by a stranger, for it involves a lack of loyalty. The spiritual life of the Christian is also true friendship with Jesus; this means it is based on loyalty and uprightness, and on being true to one's word.
Judas had already decided to hand Jesus over and had made arrangements with the chief priests (cf. Matthew 26:14; Mark 14:10-11; Luke 22:3-6). Temptation had been burrowing its way into Judas' heart for some time back, as we saw at the anointing at Bethany when he protested Mary's loving gesture; St. John commented in that connection that he did it not out of love for the poor but because he was a thief (cf. John 12:6).
23. In that period, on important occasions the customary thing was to eat reclining on a kind of divan called a "triclinium". The diner rested on his left elbow and ate with his right hand. This meant it was easy to lean on the person on one's left and talk to him without people hearing. In this verse we can see the intimacy and trust which obtained between the Master and the beloved disciple (cf. John 19:27; 20-2; 21:23), a model of Jesus' love for all His true disciples and of theirs for their Master.
26-27. The morsel which Jesus offers him is a sign of friendship and, therefore, an invitation to him to give up his evil plotting. But Judas rejects the chance he is offered. "What he received is good", St. Augustine comments, "but he received it to his own perdition, because he, being evil, received in an evil manner what is good" ("In Ioann. Evang.", 61, 6). Satan entering into him means that from that moment Judas gave in completely to the devil's temptation.
29. "These details have been recorded that we may not bear ill will against those who wrong us, but may reproach them and weep over them. Indeed, not those who are wronged, but those who do wrong deserve our tears. For the covetous man and the slanderer, and the man guilty of any other wrongdoing injure themselves most of all....] Christ repaid the man who was going to betray Him with just the opposite. For example, He washed his feet, reproved him without bitterness, censured him in private, ministered to him, allowed him to share in His table and His kiss. Yet, though Judas did not become better because of these things, Jesus Himself persevered in His course of action" (St. John Chrysostom, "Hom. on St. John", 71, 4).
30. The indication that "it was night" is not just a reference to the time of day but to darkness as an image of sin, an image of the power of darkness whose hour was beginning at that very moment (cf. Luke 22:53). The contrast between light and darkness, the opposition of good and evil, is frequently met with in the Bible, especially in the Fourth Gospel: even in the prologue we are told that Christ is the true Light which the darkness has not overcome (cf. John 1:5).
31-32. This glorification refers above all to the glory which Christ will receive once He is raised up on the cross (John 3:14; 12:32). St. John stresses that Christ's death is the beginning of His victory: His very crucifixion can be considered the first step in His ascension to His Father. At the same time it is glorification of the Father, because Christ, by voluntarily accepting death out of love, as a supreme act of obedience to the Will of God, performs the greatest sacrifice man can offer for the glorification of God. The Father will respond to this glorification which Christ offers Him by glorifying Christ as Son of Man, that is, in His holy human nature, through His resurrection and ascension to God's right hand. Thus the glory which the Son gives the Father is at the same time glory for the Son.
Christ's disciple will also find His highest motivation by identifying himself with Christ's obedience. St. Paul teaches this very clearly when he says: "Far be it from me to glory except in the cross of the Lord Jesus Christ" (Galatians 6:14).
33. From this verse onwards the evangelist recounts what is usually called the discourse of the Last Supper; in it we can distinguish three parts. In the first, our Lord begins by proclaiming the New Commandment (verses 33-35) and predicts Peter's denials (verses 36-38); He tells them that His death means His going to His Father (Chapter 14), with Whom He is one because He is God (verses 1-14); and He announces that after His resurrection He will send them the Holy Spirit, who will guide them by teaching them and reminding them of everything He told them (verses 15-31).
The second part of the discourse is contained in Chapters 15 and 16. Jesus promises to those who believe in Him a new life of union with Him, as intimate as that of a vine and its branches (15:1-18). To attain this union one must keep His New Commandment (verses 9-18). He forewarns them about the contradictions they will suffer, and He encourages them by promising the Holy Spirit who will protect them and console them (verses 18-27). The action of the Paraclete or Consoler will lead them to fulfill the mission Jesus has entrusted to them (16:1-15). The fruit of the presence of the Holy Spirit will be fullness of joy (verses 16-33).
The third part (Chapter 7) gives Jesus' priestly prayer, in which He asks the Father to glorify Him through the cross (verses 1-5). He prays also for His disciples (verses 6-19) and for all those who through them will believe in Him, so that, staying in the world without being of the world, the love of God should be in them and they should bear witness to Christ being the envoy of the Father (verses 20-26).
36-38. Once again Peter in his simplicity and sincerity tells his Master that he is ready to follow Him even to the point of dying for Him. But he is not yet ready for that. Our Lord, St. Augustine comments, "establishes here a delay; He does not destroy the hope, indeed He confirms it by saying, `You shall follow afterwards! Why are you in haste, Peter? As yet the rock has not made you strong inwardly: do not be brought down by your presumption. Now you cannot follow Me, but do not despair: later you will'" ("In Ioann. Evang.", 66, 1). Peter had certainly meant what he said, but his resolution was not very solid. Later on he would develop a fortitude based on humility; then, not considering himself worthy to die in the way his Master did, he will die on a cross, head downwards, rooting in the soil of Rome that solid stone which endures in those who succeed him and forming the basis on which the Church, which is indefectible, is built. Peter's denials, which are signs of his weakness, were amply compensated for by his profound repentance. "Let everyone draw from this example of contrition, and if he has fallen let him not despair, but always remember that he can become worthy of forgiveness" (St. Bede, "In Ioann. Evang. Expositio, in loc".).
Source: "The Navarre Bible: Text and Commentaries". Biblical text taken from the Revised Standard Version and New Vulgate. Commentaries made by members of the Faculty of Theology of the University of Navarre, Spain. Published by Four Courts Press, Kill Lane, Blackrock, Co. Dublin, Ireland. Reprinted with permission from Four Courts Press and Scepter Publishers, the U.S. publisher.