Today, Holy Thursday, has two foci: Jesus washing the feet of His disciples and the giving of His Supper. The two are not unrelated. A close reading of the foot washing text from John 13 reveals that Jesus is doing more than washing feet - He speaks of cleanness and uncleanness in a greater way. He is teaching His disciples about forgiveness and the ongoing washing away of sins that is needed. He speaks of bathing only once (baptism), but the need of the ongoing washing of the dirt collected from everyday life (absolution). He says "not all of you are clean" because He knew who would betray Him. He also says "if I do not wash you, you have no share with me." Clearly, these are all statements of a washing not just of feet, but of sin. So what Jesus is doing here is a kind of "living parable," not unlike what the prophets in the Old Testament would often do - act out the words of their teaching.
So having taught and given all this, Jesus now goes to accomplish the forgiveness that will be given through these means - He goes to the cross.