Theophylact of Ohrid
Catena Aurea · Johannesevangelium 13
So after he had washed their feet, and had taken his garments, and was set down again, he said unto them, Know ye what I have done to you? Ye call me Master and Lord: and ye say well; for so I am. If I then, your Lord and Master, have washed your feet; ye also ought to wash one another’s feet. For I have given you an example, that ye should do as I have done to you. Verily, verily, I say unto you, The servant is not greater than his lord: neither he that is sent greater than he that sent him. If ye know these things, happy are ye if ye do them. I speak not of you all: I know whom I have chosen: but that the Scripture may be fulfilled, He that eateth bread with me hath lifted up his heel against me. Now I tell you before it come, that, when it is come to pass, ye may believe that I am he. Verily, verily, I say unto you, He that receiveth whomsoever I send receiveth me; and he that receiveth me receiveth him that sent me. If then I your Lord and Master have washed your feet, ye also ought to wash one another’s feet.
This was a necessary admonition to the Apostles, some of whom were about to rise higher, others to lower degrees of eminence. That none might exult over another, He changes the hearts of all.