Augustine of Hippo — as excerpted in the Catena Aurea on John 13:6-11

“(Tr. lvi. 4) Clean all except the feet. The whole of a man is washed in baptism, not excepting his feet; but living in the world afterwards, we tread upon the earth. Those human affections then, without which we cannot live in this world, are, as it were, our feet, which connect us with human things, so that if we say we have no sin, we deceive ourselves. (1 John 1:8) But if we confess our sins, He who washed the disciples’ feet, forgives us our sins even down to our feet, wherewith we hold our converse with earth.”