On the evening of Maundy Thursday, we celebrate the Mass of the Lord's Supper, recalling the institution of the Eucharist by our Lord, on the night before he died. On this night Jesus explicitly dedicated himself to his death the next day, which would forever unite him to his people. He gave his disciples a moving discourse on their unity, and he gave them the sacrament of unity – Holy Communion – as the concrete expression of his promise to be with them always.
'Maundy' derives from the Latin Mandatum meaning commandment, and comes from the phrase our Lord used after he had washed the feet of his disciples: "A new commandment I give you, that you love one another." He expressed his love for them in that gesture of humility and service, and his action is repeated by the priest during the Liturgy.
By ancient custom, Mass is not celebrated on Good Friday, so the Sacrament is reserved on Maundy Thursday for use on the next day. At the end of the Mass it is carried in a sloemn procession to an Altar of Repose where, honoured by lights and flowers, it is kept until the next day.
Then the altars are stripped-– symbolic of the stripping of Christ before his crucifixion. This is done without ceremony as a watch before the Blessed Sacrament begins. Those leaving the church at this point are asked to do so in silence.
The watch is kept until midnight, recalling our Lord's agony in the garden of Gethsemane, and offering prayer for the world for which he died. The watch ends with a short service of Compline at midnight.