Jesus was teaching His disciples that once they had been cleansed from their sins by Him (in which they were made fully clean) they only needed thereafter to be cleansed from the daily contamination of living in a sinful world - from the stumbles and sins that every believer still experiences and and commits while living on earth. He likens this to needing only to wash our feet if we have taken a bath. This incident provides an important principle for our daily walking with the Lord.
It is often said that the Lord's Day is like an oasis for the saint as he or she travels through the barren wilderness of the world - a place to be refreshed, cleansed and renewed before journeying onwards to heaven. In this sense, our pilgrimage to glory is punctuated every week with wonderful watering places, provided by the grace of our God in His wisdom as the One Who made us and knows our weakness. This is where we feed, where we drink, where we wash our soiled garments and get ready for another week of travel.
If this is true of the Lord's Day, then it is also true that the midweek prayer meeting in a church offers a similar opportunity for us. Here, we may withdraw from the world and get our focus back on Christ. Here we may confess our sins and find cleansing. Here we may be strengthened through the Word and blessed with the fellowship of our brothers and sisters.
Which desert traveler is there who would deliberately and knowingly skirt around a watering hole and travel on in a dirty, dusty and weakened condition to the next one? In the same way, why would we deny ourselves a wonderful opportunity for spiritual refreshment in between Lord's Days? Let's make the most of every opportunity that we have to profit from the means of grace as we journey on to the celestial city!