Symbols point beyond themselves to something deeper.
It reminds us of His daily cleansing in our lives, the celebration awaiting us in heaven, and the price He paid so we could have eternal life. This first part of communion reminds us of our need for daily cleansing from sin. It's a time of introspection and self-examination. Washing feet as a symbol of this isn't something thought of by the Church or the Apostles. It's something Jesus asked us to do.