It was at the Feast of the Passover, (or last supper), Jesus dramatically subverted the symbolism by washing his disciple's feet.
'(He) rose from supper, laid aside his garments, and girded himself with a towel. Then he poured water into a basin , and began to wash the disciples' feet, and to wipe them with the towel which he was girded.'
John 13: 4,5
'I have done this to give you an example of something that you should do.'
Christ's action has been generally interpreted as a demonstration that service rather than status would represent greatness in the Kingdom of Heaven. Also by this action he prepared his disciples (and their converts) to walk in the path of righteousness.
'If I then, your Lord and Master, have washed your feet, ye also ought to wash one another's feet. For I have given you an example , that ye should do as I have done to you.'
John 13: 14,15