Council of Trent: Session 22
Chapter 2
That the Sacrifice of the Mass is propitiatory both for the living and the dead.
And forasmuch as, in this divine sacrifice which is celebrated in the mass, that same Christ is contained and immolated in an unbloody manner, who once offered Himself in a bloody manner on the altar of the cross; the holy Synod teaches, that this sacrifice is truly propitiatory and that by means thereof this is effected, that we obtain mercy, and find grace in seasonable aid, if we draw nigh unto God, contrite and penitent, with a sincere heart and upright faith, with fear and reverence. For the Lord, appeased by the oblation thereof, and granting the grace and gift of penitence, forgives even heinous crimes and sins. For the victim is one and the same, the same now offering by the ministry of priests, who then offered Himself on the cross, the manner alone of offering being different. The fruits indeed of which oblation, of that bloody one to wit, are received most plentifully through this unbloody one; so far is this (latter) from derogating in any way from that (former oblation). Wherefore, not only for the sins, punishments, satisfactions, and other necessities of the faithful who are living, but also for those who are departed in Christ, and who are not as yet fully purified, is it rightly offered, agreeably to a tradition of the apostles.
Chapter 3
On Masses in honour of the Saints.
And although the Church has been accustomed at times to celebrate, certain masses in honour and memory of the saints; not therefore, however, doth she teach that sacrifice is offered unto them, but unto God alone, who crowned them; whence neither is the priest wont to say, "I offer sacrifice to thee, Peter, or Paul;" but, giving thanks to God for their victories, he implores their patronage, that they may vouchsafe to intercede for us in heaven, whose memory we celebrate upon earth.
Chapter 4
On the Canon of the Mass.
And whereas it beseemeth, that holy things be administered in a holy manner, and of all holy things this sacrifice is the most holy; to the end that it might be worthily and reverently offered and received, the Catholic Church instituted, many years ago, the sacred Canon, so pure from every error, that nothing is contained therein which does not in the highest degree savour of a certain holiness and piety, and raise up unto God the minds of those that offer. For it is composed, out of the very words of the Lord, the traditions of the apostles, and the pious institutions also of holy pontiffs.
Chapter 5
On the solemn ceremonies of the Sacrifice of the Mass.
And whereas such is the nature of man, that, without external helps, he cannot easily be raised to the meditation of divine things; therefore has holy Mother Church instituted certain rites, to wit that certain things be pronounced in the mass in a low, and others in a louder, tone. She has likewise employed ceremonies, such as mystic benedictions, lights, incense, vestments, and many other things of this kind, derived from an apostolical discipline and tradition, whereby both the majesty of so great a sacrifice might be recommended, and the minds of the faithful be excited, by those visible signs of religion and piety, to the contemplation of those most sublime things which are hidden in this sacrifice.