Try this on for size:
If one looks beyond the simple historical narrative that occurs in this passage from the Gospels, there is a clear reference to Baptism and Confession. Our Lord tells St. Peter that if one is not washed by Him (ie, undergoes Baptism), then one has no part in Him. But, note that Our Lord does not stop there. He says that those who are clean (those who have been Baptised) do not need to wash, except for the feet.
In the ancient world, the feet were always the filthiest parts of the body, since they walked through dust, grime and excrement daily. It was common courtesy and simple hygeine for one to either wash one's own feet or have them washed by a servant before entering another's house or a place of worship. How does this apply to us, though?
As believers, we who have been washed in the waters of Baptism have been cleansed from all previous sins and from the stain of the world which we were born into. However, we still walk through the filth and ordure of sin every day, and though we are clean, we still need to cleanse our souls of the sins which we daily, hourly, and minutely commit, especially before we draw nigh unto the Lord in worship.
Through the words of Christ to His Apostles granting them the authority to forgive sins as Christ's emissaries on earth, which power was passed to their sucessors, even to the present day, we are given the opportunity to have our feet washed by the Saviour Himself, as those same Apostles were. One would have to be a fool not to avail himself of this opportunity at every possible time.
Call me an Origenist, but I consistently see deeper, spiritual meanings behind the obvious meaning in a text.
+IC XC NIKA+
Phillip.