We need to understand some background here. Jesus and His disciples met for a Seder a day early. In that day and time, it was typical for professional groups and similar private clubs to meet like this, just men without their families. The regular Passover Meal took place about 24 hours later with families. Thus, for Jesus and His disciples to meet like this was frankly common. At the same time, it signified that they were not quite vested as a covenant household just yet. Were Jesus actually reigning as the Messiah, the same group might well celebrate the Seder together and with their families, as if they were one clan. This is how a royal staff acted.
So this was a professional group not yet announcing itself as a ruling court. The Twelve were starting to expect this Messiah stuff would happen just about any day now. They would have been horrified at the idea that this was the last Passover supper for Jesus in the flesh.
So they gathered in the Upper Room, which we know is somewhere near the eastern wall of Jerusalem, and also near one of the gates. Jesus’ ministry had several wealthy donors, and this household appears to have been quite wealthy, but not part of the old Jerusalem blue-bloods. For reasons unknown, the host didn’t provide a Gentile slave to wash their feet. Jews could wash their own feet, but it was forbidden have a Jewish servant or slave wash the feet of guests. Apparently the water and basin was provided, but for some reason the disciples gathered in the Upper Room with Jesus having neglected this standard ritual before the meal.
The context of the passage indicates the meal itself was finished, but not the final few rituals involving the table settings. Before carrying on with the ritual ending, Jesus rose from His place at the table and took off His street clothes. He then wrapped a towel around His waist and prepared to wash their feet. Keep in mind that this was a traditional Hebrew seating pattern, with the men around the table lounging on big fat cushions with their heads close to the table, and their feet out away from the it. All of them were skewed at an angle from the table, but parallel to each other so they could eat their right hands and lean on their left elbows.
Jesus came around with the basin of water, the towel around His waist, and at least one smaller vessel for dipping and pouring the water over their feet. He would then wipe off the wet feet with the towel around His waist. So nobody else had to move, just tolerate Him doing this, since they would have kicked off their sandals upon entering the room, at the least, if not upon entering the house.
Peter objected. There’s nothing going on here with secret symbolism. Jesus was performing a degrading act, reducing Himself to no more than an unconverted Gentile slave. Peter was embarrassed by this. Jesus said He understood how Peter felt, and that eventually this would make sense some day in the future. For now, Jesus had something He really needed to do here, because unknown to all but Judas and Jesus, time was short. This was His last meal before the Cross.
Peter still objected. Jesus warned him that it didn’t matter how he felt. If he didn’t go along with it, he would not be part of the Messianic Court. Looking for some way to preserve his grip on the situation, Peter asked that the other exposed parts of him would be washed. If we are going to do this, let’s do it right. Peter knew he needed cleansing.
Jesus kept it simple. Peter had taken a bath that day, so it wasn’t necessary to get his hands and face in the same water that washes twelve pairs of dirty feet. Then He said something that changed the nature of the act. He changed the symbolism of bathing into ritual washing, and pronounced them pure enough to serve Him, but not every one one of them. John, as the younger cousin of Jesus and likely His closest buddy, caught on to the reference and noted it.
Jesus finished the task, put His clothes back on, and reclined once more on His cushion at the table. Sure enough, He proceeded to turn this into a lesson for them. If He, as their Master, could set aside His privileges to do something that was a virtual necessity for them, surely they could learn to ditch their Jewish arrogance long enough to serve each other in various ways.
If they could just figure this out, everything else He was about to do would make more sense to them. The necessity of serving your fellow servants in the Kingdom, treating the unworthy as worthy in certain key areas of life, it would bring about the redemption of God. It would bless them with divine glory.
One final note: We happen to know from the other Gospels that they had been arguing with each other on the way to the meeting. By washing their feet, Jesus deflated all their hard feelings. He needed them to listen to what He was going to say next.