Jesus was washing his disciples' feet when Peter in his enthusiasm suggested that Jesus wash not just his feet but his hands and head as well. Jesus replied, "A person who has had a bath needs only to wash his feet; his whole body is clean. And you are clean, though not every one of you." (John 13:10)
The meaning in this story told in John 13, as I heard it today, beyond the very important meaning of Jesus' example of service that He expects us to emulate by serving one another, and beyond His recognition that one of the disciples was soiled in his heart, is that we who follow Jesus have been cleansed in our spirits in a way that does not require repetition. We don't need to be saved, or wholly cleansed, repeatedly or regularly.
However, because we walk through the world, not as striclty spiritual beings as we will be in Heaven but as fleshly creatures, we pick up the filth and pollution of the world on our feet. That is, the part of us that touches the world, dominion of the enemy, must be regularly attended to with cleansing. Even clean, we continue to sin.
The task Jesus sets before us in His example of washing our feet is to attend to one another's spiritual cleanliness within the context of having been wholly saved. We must encourage one another in regular repenting in order to cleanse ourselves of the filth of sin we accumulate from walking in the world. We must participate in one another's cleansing process, as one body, as a family with no secrets, as members who trust one another with their dirty feet.