In "Word Focus" Darrell Grim writes:

The Rabbinical customs prescribed that after the passing of the cup, the head of the group was to rise and wash his hands. It was probably at this point that Christ rose from the table. However, He departed from the traditional hand washing and adapted it to foot washing. Christ was injecting a very practical and relevant principle into the liturgical humdrum that was a part of the Jewish feasts. He was, throughout this feast, transforming it from the Paschal meal to the Eucharist. He was the fulfillment of all that the Paschal meal represented.

Discussion: What are other similarities and differences we see between the Passover feast and the Last Supper?
Source: Jesus, Son of God: Adult Teacher's Insights, page 46.