“For he knew who should betray him; therefore said he, Ye are not all clean.”
John 13:11 — Greek Interlinear
Church Fathers on John 13:11
As a physician, who has many sick under his care, begins with those who want his attention most, so Christ, in washing His disciples’ feet, begins with the most unclean, and so comes at last to Peter, who needed the washing less than any: Then comes He to Simon Peter. Peter resisted being washed, perhaps because his feet were nearly clean: and Peter said to Him, Lord, do you wash my feet?
What is the meaning of you and my feet? It is better to think than speak of this; lest one should fail in explaining adequately what might have been rightly conceived.
Though Peter was the first of the Apostles, yet it is possible that the traitor petulantly placed himself above him; and that this may be the reason why our Lord first began to wash, and then comes to Peter.