From: John 13:16-20
Jesus Washes His Disciples' Feet
(Jesus said to His disciples,)  "Truly, truly, I say to you, a servant is not greater than his master; nor is he who is sent greater than he who sent him.  If you know these things, blessed are you if you do them.  I am not speaking to you all; I know whom I have chosen; it is that the Scripture may be fulfilled, `He who ate my bread has lifted his heel against me.'  I tell you this now, before it takes place, that when it does take place you may believe that I am He.  Truly, truly, I say to you, he who receives any man whom I send receives Me; and he who receives Me receives Him who sent Me."
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).
18. Lifting one's heel against someone means hitting him brutally; metaphorically, therefore, it means violent enmity. Judas' treachery fulfills the words of Psalm 41:10 where the psalmist complains bitterly of a friend's treachery. Once again the Old Testament prefigures events which find their full _expression in the New.
Through Baptism, the Christian has become a son of God and is called to share in God's good things, not only in Heaven but also on earth: He has received grace, he shares in the Eucharistic Banquet..., he shares with his brethren, other Christians, the friendship of Jesus. Therefore, if a person sins who has been born again through Baptism, in some sense his is a sort of treachery similar to Judas'. However, we have the recourse of repentance: if we trust in God's mercy we can set about recovering our friendship with God.
"React. Listen to what the Holy Spirit tells you: `"Si inimicus meus maledixisset mihi, sustinuissem utique"'. If it were the enemy who insulted me, I could put up with that. But you...`"tu vero homo unanimis, dux meus, et notus meus, qui simul mecum dulces capiebas cibos"': you, My friend, My Apostle, who sit at My table and take sweet food with Me!" ([St] J. Escriva, "The Way", 244).
19. Jesus tells the Apostles in advance about Judas' treachery, so that when they see Christ's predictions come true, they will realize He has divine knowledge and that in Him are fulfilled the Scriptures of the Old Testament (cf. John 2:22). On the words "I am", cf. note on John 8:21-24.
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.