John 13:6 - Albert Barnes' Notes on the Bible

Dost thou wash my feet? - Every word here is emphatic. Dost thou - the Son of God, the Messiah - perform the humble office of a servant - toward me, a sinner? This was an expression of Peter’s humility, of his reverence for Jesus, and also a refusal to allow him to do it. It is possible, though not certain from the text, that he came to Simon Peter first.