Jesus gave us the Sacrament of the Holy Eucharist at the Last Supper, the night before He died. He said, "This is My Body", and "This is My Blood." The bread and wine are changed into His Holy Body and His Holy Blood at every Mass. He gave the command "Do this in remembrance of me. At that moment, the power is given to priests to change the bread and wine into the Body and Blood of Jesus.