Origen
Catena Aurea · Johannesevangelium 13
Then cometh he to Simon Peter: and Peter said unto him, Lord, dost thou wash my feet? Jesus answered and said unto him, What I do thou knowest not now; but thou shalt know hereafter. Peter saith unto him, Thou shalt never wash my feet. Jesus answered him, If I wash thee not, thou hast no part with me. Simon Peter saith unto him, Lord, not my feet only, but also my hands and my head. Jesus saith to him, He that is washed needeth not save to wash his feet, but is clean every whit: and ye are clean, but not all. For he knew who should betray him; therefore said he, Ye are not all clean. Jesus answered and said unto him, What I do thou knowest not now; but thou shalt know hereafter.
(t. xxxii. 6.) Ye are clean, refers to the eleven; but not all, to Judas. He was unclean, first, because he cared not for the poor, but was a thief; secondly, because the devil had put it into his heart to betray Christ. Christ washes their feet after they are clean, shewing that grace goes beyond necessity, according to the text, He that is holy, let him be holy still. (Apoc. 22:11)