The three days" are the most holy of the liturgical year because they commemorate the Institution of the Lord's Supper (Eucharist and Priesthood) in the Upper Room, with its mandatum/command to "wash the feet" of others in imitation of Jesus Christ; the Passion of the Lord, who suffered and died on the cross on Calvary for the sake of our salvation; and Holy Saturday, when we "vigil" in anticipation of the Easter joy that comes to the world through the Resurrection of Christ from the dead.