Jesus took the disciples' feet and washed each sole. Eventually, Jesus reached Peter, who had some questions regarding the feet washing.
Peter asked Jesus if He is going to wash Peter's feet. The question implies that Peter does not understand the point and purpose of Jesus washing the disciples feet (especially with a comment from Jesus). But Jesus promised Peter that he would know afterward, even if Peter does not know the point at that time. Today, even if we don't know Jesus's exact purpose for doing something, that doesn't necessarily mean we can't know eventually. In the meantime, we should let Jesus work.