Holy Thursday

Holy Thursday is the most complex and profound of all religious observances, saving only the Easter Vigil. It celebrates both the institution by Christ himself of the Eucharist and of the institution of the sacerdotal priesthood (as distinct from the 'priesthood of all believers') for in this, His last supper with the disciples, a celebration of Passover, He is the self-offered Passover Victim, and every ordained priest to this day presents this same sacrifice, by Christ's authority and command, in exactly the same way. The Last Supper was also Christ's farewell to His assembled disciples, some of whom would betray, desert or deny Him before the sun rose again.

https://www.catholicnewsagency.com/saint/holy-thursday-675