From: John 13:1-15
Jesus Washes His Disciples' Feet
 Now before the feast of the Passover, when Jesus knew that His hour had come to depart out of this world to the Father, having loved His own who were in the world, He loved them to the end.  And during supper, when the devil had already put it into the heart of Judas Iscariot, Simon's son, to betray Him,  Jesus, knowing that the Father had given all things into His hands, and that He had come from God and was going to God,  rose from supper, laid aside His garments, and girded Himself with a towel.  Then He poured water into a basin, and began to wash the disciples' feet, and to wipe them with the towel with which He was girded.  He came to Simon Peter; and Peter said to Him, "Lord, do You wash my feet?"  Jesus answered him, "What I am doing you do not know now, but afterward you will understand."  Peter said to Him, "You shall never wash my feet." Jesus answered him, "If I do not wash you, you have no part in Me."  Simon Peter said to Him, "Lord, not my feet only but also my hands and my head!"  Jesus said to him, "He who has bathed does not need to wash, except for his feet, but he is clean all over; and you are clean, but not all of you."  For He knew who was to betray Him; that was why He said, "You are not all clean."
 When He had washed their feet, and taken His garments, and resumed His place, He said to them, "Do you know what I have done for you?  You call Me Teacher and Lord; and you are right, for so I am.  If then your Lord and Teacher have washed your feet, you also ought to wash one another's feet.  For I have given you an example, that you also should do as I have done for you."
1. Jewish families sacrificed a lamb on the eve of the Passover, in keeping with God's command at the time of the exodus from Egypt when God liberated them from the slavery of Pharaoh (Exodus 12:3-14; Deuteronomy 16:1-8). This liberation prefigured that which Jesus Christ would bring about--the redemption of men from the slavery of sin by means of His sacrifice on the cross (cf. 1:29). This is why the celebration of the Jewish Passover was the ideal framework for the institution of the new Christian Passover.
Jesus knew everything that was going to happen; He knew His death and resurrection were imminent (cf. 18:4); this is why His words acquire a special tone of intimacy and love towards those whom He is leaving behind in the world. Surrounded by those whom He has chosen and who have believed in Him, He gives them His final teachings and institutes the Eucharist, the source and center of the life of the Church. "He Himself wished to give that encounter such a fullness of meaning, such a richness of memories, such a moving image of words and thoughts, such a newness of acts and precepts, that we can never exhaust our reflection and exploration of it. It was a testamentary supper, infinitely affectionate and immensely sad, and at the same time a mysterious revelation of divine promises, of supreme visions. Death was imminent, with silent omens of betrayal, of abandonment, of immolation; the conversation dies down but Jesus continues to speak in words that are new and beautifully reflective, in almost supreme intimacy, almost hovering between life and death" ([Pope] Paul VI, "Homily on Holy Thursday", 27 March 1975).
What Christ did for His own may be summed up in this sentence: "He loved them to the end." It shows the intensity of His love--which brings Him even to give up His life (cf. John 15:13); but this love does not stop with His death, for Christ lives on and after His resurrection He continues loving us infinitely: "It was not only thus far that He loved us, who always and forever loves us. Far be it from us to imagine that He made death the end of His loving, who did not make death the end of His living" (St. Augustine, "In Ioann. Evang.", 55, 2).
2. The Gospel shows us the presence and activity of the devil running right through Jesus' life (cf. Matthew 4:1-11; Luke 22:3; John 8:44; 12:31; etc.). Satan is the enemy (Matthew 13:39), the evil one (1 John 2:13). St. Thomas Aquinas (cf. "Commentary on St. John, in loc.") points out that, in this passage, on the one hand, we clearly see the malice of Judas, who fails to respond to this demonstration of love, and on the other hand great emphasis is laid on the goodness of Christ, which reaches out beyond Judas' malice by washing his feet also and by treating him as a friend right up to the moment when he betrays Him (Luke 22:48).
3-6. Aware that He is the Son of God, Jesus voluntarily humbles Himself to the point of performing a service appropriate to household servants. This passage recalls the Christological hymn in St. Paul's Letter to the Philippians: "Christ Jesus, who, though He was in the form of God, did not count equality with God a thing to be grasped, but emptied Himself, taking the form of a servant..." (Philippians 2:6-7).
Christ had said that He came to the world not to be served but to serve (Mark 10:45). In this scene He teaches us the same thing, through specific example, thereby exhorting us to serve each other in all humility and simplicity (cf. Galatians 6:2; Philippians 2:3). "Once again He preaches by example, by His deeds. In the presence of His disciples, who are arguing out of pride and vanity, Jesus bows down and gladly carries out the task of a servant.[...] This tactfulness of our Lord moves me deeply. He does not say: `If I do this, how much more ought you to do?' He puts Himself at their level, and He lovingly chides those men for their lack of generosity.
"As He did with the first twelve, so also, with us, our Lord can and does whisper in our ear, time and again: `exemplum dedi vobis' (John 13:15), I have given you an example of humility. I have become a slave, so that you too may learn to serve all men with a meek and humble heart" ([St] J. Escriva, "Friends of God", 103).
Peter understands particularly well how thoroughly our Lord has humbled Himself, and he protests, in the same kind of way as he did on other occasions, that he will not hear of Christ suffering (cf. Matthew 8:32 and par.). St. Augustine comments: "Who would not shrink back in dismay from having his feet washed by the Son of God....You? Me? Words to be pondered on rather than spoken about, lest words fail to express their true meaning" (St. Augustine, "In Ioann. Evang.", 56, 1).
7-14. Our Lord's gesture had a deeper significance than St. Peter was able to grasp at this point; nor could he have suspected that God planned to save men through the sacrificing of Christ (cf. Matthew 16:22 ff). After the Resurrection the Apostles understood the mystery of this service rendered by the Redeemer: by washing their feet, Jesus was stating in a simple and symbolic way that He had not come "to be served but to serve". His service, as He already told them, consists in giving "His life as a ransom for many" (Matthew 20:28; Mark 10:45).
Our Lord tells the Apostles that they are now clean, for they have accepted His words and have followed Him (cf. 15:3)--all but Judas, who plans to betray Him. St. John Chrysostom comments as follows: "You are already clean because of the word that I have spoken to you. That is: You are clean only to that extent. You have already received the Light; you have already got rid of the Jewish error. The Prophet asserted: `Wash yourselves; make yourselves clean; remove the evil from your souls' (Isaiah 1:16).... Therefore, since they had rooted evil from their souls and were following Him with complete sincerity, He declared, in accordance with the Prophet's words: `He who has bathed is clean all over'" (St. John Chrysostom, "Hom. on St. John", 70, 3).
15-17. Jesus' whole life was an example of service towards men, fulfilling His Father's will to the point of dying on the Cross. Here our Lord promises us that if we imitate Him, our Teacher, in disinterested service (which always implies sacrifice), we will find true happiness which no one can wrest from us (cf. 16:22; 17:13). "`I have given you an example', He tells His disciples after washing their feet, on the night of the Last Supper. Let us reject from our hearts any pride, any ambition, any desire to dominate; and peace and joy will reign around us and within us, as a consequence of our personal sacrifice" ([St] J. Escriva, "Christ Is Passing By", 94).
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.