Peter said: 'Thou shalt never wash my feet!' Our Lord replied: 'If I wash thee not, thou shalt have no part with me.' Then Peter exclaimed: 'Lord, not only my feet, but also my hands and my head.' Jesus replied: 'He that is washed, needeth not but to wash his feet, but is clean wholly.

And you are clean, but not all.' By these last words he referred to Judas.

He had spoken of the washing of the feet as signifying purification from daily faults, because the feet, which are continually in contact with the earth, are also continually liable to be soiled, unless great care is taken.
This washing of the feet was spiritual, and served as a species of absolution.

Peter, in his zeal, saw nothing in it but too great an act of abasement on the part of his Master; he knew not that to save him Jesus would the very next day humble himself even to the ignominious death of the cross.
When Jesus washed the feet of Judas, it was in the most loving and affecting manner; he bent his sacred face even on to the feet of the traitor; and in a low voice bade him now at least enter into himself, for that he had been a faithless traitor for the last year.

Judas appeared to be anxious to pay no heed whatever to his words, and spoke to John, upon which Peter became angry, and exclaimed: 'Judas, the Master speaks to thee!' Then Judas made our Lord some vague, evasive reply, such as, 'Heaven forbid, Lord!' The others had not remarked that Jesus was speaking to Judas, for this words were uttered in a low voice, in order not to be heard by them, and besides, they were engaged in putting on their shoes.