First, if so, wasn’t it cruel of our loving saviour to condemn Peter to having no part with him simply because he didn’t want to play along. Some insist that Peter would still have a part with Jesus nonetheless. However, that would reduce Jesus to, at best, a weakling with the need to resort to empty threat to get his way; or, at worst, a liar.
Second, the disciples did not understand it as an object lesson because as stated above the church actually administered footwashing.