The Holy Thursday Mass of the Lord's Supper features St. John's account of that Supper, which does not mention the institution of the Eucharist. Jesus does establish the priesthood, in terms sacrificial: His Body and Blood are at the disposal of His servants. The Master washes their feet and directs the Apostles to "go and do likewise" in what has come to be known as the Mandatum ("commandment," mitzvah in Hebrew; hence the alternate name "Maundy" Thursday). Peter, who often speaks as the first among the Apostles, initally chafes at this self-emptying display; but his vehement resistance becomes a vehement insistence when Jesus reminds him that to let Jesus serve him thus is a condition for sharing in the Kingdom. "Master, then not only my feet, but my hands and head as well" (Jn 13:9): as if to say, "Everything in me that is needed to render Your kind of service needs to be cleansed if I am to do it."
It is a powerful display, this mandatum: the priest usually removes his chasuble (outer garment), and with pitcher and basin in hand reminds the people of God that his own will and sensibilities must be purified of self-importance. Any attitudes that have perpetuated the popular perception of priests as center of the parochial universe must be smashed just like the alabaster jar that a woman smashed in order to release its fragrant oils upon the Lord's sacred Head (cf. Mark 14:3)
The remainder of the Mass resembles every other: it is the tangible self-gift of God-in-flesh, where bread and wine are changed, their substance now giving Life to the world and meaning to every authentic human offering. At the end of the Mass, the Eucharist is transferred to an "out-of-the-way place," setting the sanctuary stage for the memorial of Jesus' Passion and Death. The assembly abides and eventually (without formal dismissal, whenever each is ready) leaves in contemplative silence.