It is first of all necessary to make clear that in every sacrifice of the Mass four distinct categories of persons really participate.
(1) At the head of all stands of course the High Priest, Christ Himself; to make the Sacrifice of the Cross fruitful for us and to secure its application, He offers Himself as a sacrifice, which is quite independent of the merits or demerits of the Church, the celebrant or the faithful present at the sacrifice.
(2) Next after Christ, and in the second place, comes the Church as a juridical person, who, according to the express teaching of the Council of Trent has received from the hands of her Divine Founder the institution of the Mass and also the commission to ordain priests and to have celebrated by these the most venerable Sacrifice. This intermediate stage between Christ and the celebrant may be neither passed over nor eliminated, since a bad and immoral priest, as an ecclesiastical official, does not offer up his own sacrifice -- which indeed could only be impure -- but the immaculate Sacrifice of Christ and His spotless Bride, which can be soiled by no wickedness of the celebrant. However, the greatness and extent of this ecclesiastical service is dependent on the greater or less holiness of the reigning pope, the bishops, and the clergy throughout the World, and for this reason in times of ecclesiastical decay and laxity of morals (especially at the papal court and among the episcopate) the fruits of the Mass, resulting from the sacrificial activity of the Church, might under certain circumstances, easily be very small.
(3) With Christ and His Church is associated in third place the celebrating priest, since he is the representative through whom the real and the mystical Christ offer up the sacrifice. If, therefore, the celebrant be a man of great personal devotion, holiness, and purity, there will accrue an additional fruit which will benefit not himself alone, but also those in whose favor he applies the Mass.
(4) Finally, in the fourth place, must be mentioned those who participate actively in the Sacrifice of the Mass, e.g., the servers, lectors, organist, singers, and the whole congregation joining in the sacrifice. The more fervent the prayer, the richer the fruit. Most intimate is the active participation in the Sacrifice of those who receive Holy Communion during the Mass, since in their case the special fruits of the Communion are added to those of the Mass.read...