CANON I.--If any one saith, that in the mass a true and proper sacriflce is not offered to God; or, that to be offered is nothing else but that Christ is given us to eat; let him be anathema.
Forasmuch as, under the former Testament, according to the testimony of the Apostle Paul, there was no perfection, because of the weakness of the Levitical priesthood; there was need, God, the Father of mercies, so ordaining, that another priest should rise, according to the order of Melchisedech, our Lord Jesus Christ, who might consummate, and lead to what is perfect, as many as were to be sanctified. He, therefore, our God and Lord, though He was about to offer Himself once on the altar of the cross unto God the Father, by means of his death, there to operate an eternal redemption; nevertheless, because that His priesthood was not to be extinguished by His death, in the last supper, on the night in which He was betrayed,--that He might leave, to His own beloved Spouse the Church, a visible sacrifice, such as the nature of man requires, whereby that bloody sacrifice, once to be accomplished on the cross, might be represented, and the memory thereof remain even unto the end of the world, and its salutary virtue be applied to the remission of those sins which we daily commit,--declaring Himself constituted a priest for ever, according to the order of Melchisedech, He offered up to God the Father His own body and blood under the species of bread and wine; and, under the symbols of those same things, He delivered (His own body and blood) to be received by His apostles, whom He then constituted priests of the New Testament; and by those words, Do this in commemoration of me, He commanded them and their successors in the priesthood, to offer (them); even as the Catholic Church has always understood and taught.
For, having celebrated the ancient Passover, which the multitude of the children of Israel immolated in memory of their going out of Egypt, He instituted the new Passover, (to wit) Himself to be immolated, under visible signs, by the Church through (the ministry of) priests, in memory of His own passage from this world unto the Father, when by the effusion of His own blood He redeemed us, and delivered us from the power of darkness, and translated us into his kingdom. And this is indeed that clean oblation, which cannot be defiled by any unworthiness, or malice of those that offer (it); which the Lord foretold by Malachias was to be offered in every place, clean to his name, which was to be great amongst the Gentiles; and which the apostle Paul, writing to the Corinthians, has not obscurely indicated, when he says, that they who are defiled by the participation of the table of devils, cannot be partakers of the table of the Lord; by the table, meaning in both places the altar. This, in fine, is that oblation which was prefigured by various types of sacrifices, during the period of nature, and of the law; in as much as it comprises all the good things signified by those sacrifices, as being the consummation and perfection of them all.
--With thanks to CABH