Q. On Holy Thursday, by what act and/or word did Jesus institute holy orders?
A. Here is a reply from Father Francis Hoffman, J.C.D.:
When Jesus gave the order, “Do this in memory of me” (Lk 22:19), he instituted the Sacrament of Holy Orders. It is true that Jesus gave additional “orders” to the apostles at other times, but this one is so closely connected to the holy Eucharist — the source and summit of life in the Church — that many theologians consider it the most probable answer on the subject. This took place at the Last Supper, immediately after Jesus had changed the bread and wine into His Body and Blood. This event is narrated in the Gospels of Matthew (see 26:17-30), Mark (14:12-26) and Luke (22:7-38).
The Catechism of the Catholic Church points out: “The one sent by the Lord does not speak and act on his own authority, but by virtue of Christ’s authority; not as a member of the community, but speaking to it in the name of Christ. No one can bestow grace on himself; it must be given and offered. This fact presupposes ministers of grace, authorized and empowered by Christ. From him, bishops and priests receive the mission and faculty (“the sacred power”) to act in persona Christi Capitis” (No. 875).