Catechism Council of Trent
“Form To Be Used In The Consecration Of The Wine
With regard lo the consecration of the wine, which is the other element of this Sacrament, the priest, for the reason we have already assigned, ought of necessity to be well acquainted with, and well understand its form. We are then firmly to believe that it consists in the following words: This is the chalice of my blood, of the new and eternal testament, the mystery of faith, which shall be shed for you and for many, to the remission of sins. Of these words the greater part are taken from Scripture; but some have been preserved in the Church from Apostolic tradition.
Thus the words, this is the chalice, are found in St. Luke and in the Apostle; but the words that immediately follow, of my blood, or my blood of the new testament, which shall be shed for you and for many to the remission of sins, are found partly in St. Luke and partly in St. Matthew. But the words, eternal, and the mystery of faith, have been taught us by holy tradition, the interpreter and keeper of Catholic truth.Concerning this form no one can doubt, if he here also attend to what has been already said about the form used in the consecration of the bread. The form to be used (in the consecration) of this element, evidently consists of those words which signify that the substance of the wine is changed into the blood of our Lord. since, therefore, the words already cited clearly declare this, it is plain that no other words constitute the form.
They moreover express certain admirable fruits of the blood shed in the Passion of our Lord, fruits which pertain in a most special manner to this Sacrament. Of these, one is access to the eternal inheritance, which has come to us by right of the new and everlasting testament. Another is access to righteousness by the mystery of faith; for God hath set forth Jesus to be a propitiator through faith in his blood, that he himself may be just, and the justifier of him, who is of the faith of Jesus. Christ. A third effect is the remission of sins.”
LATERAN COUNCIL III 1179
414-415 “You have asked (indeed) who has added to the form of the words which Christ Himself expressed when He changed the bread and wine into the body and blood, that in the Canon of the Mass which the general Church uses, which none of the Evangelists is read to have expressed. . . . In the Canon of the Mass that expression, "mysterium fidei,"is found interposed among His words. . From the expression, moreover, concerning which your brotherhood raised the question, namely “mysterium fidei,” certain people have thought to draw a protection against error… Yet “mysterium fidei” is mentioned, since something is believed there other than what is perceived; and something is perceived other than is believed… Therefore, we believe that the form of words, as is found in, the Canon, the Apostles received from Christ, and their successors from them. . . .