The story of the washing of the feet is told only in John's Gospel. It is the main action at the Last Supper. (John's account of the Last Supper does not mention the bread and the wine. Reference to the body and blood of Jesus as food and drink are found earlier in John - in chapter six, the "Bread of Life" chapter.)
The foot-washing is a remarkable action on the part of Jesus. It was proper hospitality for the host to provide water for the guests to wash their feet. But actually to wash their feet is something not even a slave could be required to do by his master.
Something changed in the Upper Room that night. The bread and the wine were changed into the body and blood of Jesus. But something else was changed, never to be the same again.
When Jesus washed the feet of his disciples, all better-than-thou distinctions were washed away. In case you have any doubt about that, John is clear that Judas was still at the supper table when this happened.
Jesus washed Judas' feet.
There is no more to say. (Well, yes, there is. The Lord and you need to have a serious conversation.)
- Little White Book, Diocese of Saginaw