67 Christ the Lord, "Eternal Priest according to the order of Melchisedech," "loving His own who were of the world," "at the last supper, on the night He was betrayed, wishing to leave His beloved Spouse, the Church, a visible sacrifice such as the nature of men requires, that would re-present the bloody sacrifice offered once on the cross, and perpetuate its memory to the end of time, and whose salutary virtue might be applied in remitting those sins which we daily commit, . . . offered His body and blood under the species of bread and wine to God the Father, and under the same species allowed the apostles, whom he at that time constituted the priests of the New Testament, to partake thereof; commanding them and their successors in the priesthood to make the same offering."
Source: Mediator Dei (Vatican.va)