The Sacrifice of the Mass is the great devotion of the Catholic Church, and, of all means to assist the souls in Purgatory, none is more valuable or meritorious; for there Jesus Christ offers Himself and His infinite merits to His Heavenly Father, by the hands of the priest, in behalf of the suffering souls. The unbloody Sacrifice of the Mass does not essentially differ from the sacrifice of the cross, but only accidentally as to the mode of oblation, and no limit can be placed to the effect of this great sacrifice, which contains in itself all graces.
From this inestimable efficacy, however, we may not infer that the offering of one Mass is sufficient to release the souls we love; for, though the Sacrifice on Calvary was infinite, we cannot conclude that the application of it, through the Mass, must also be infinite. St. Thomas Aquinas tells us, it was not the intention of Jesus Christ to bestow the full efficacy of His suffering and death, which is celebrated in every Mass, upon us; His merits are applied according to His Adorable Will, for the ways of God are often inscrutable.
It is very salutary, therefore, to have the Holy Sacrifice offered frequently for the repose of a soul. Should the souls who are dear to us, for whom we intercede in this manner, be already in the enjoyment of eternal bliss, Divine wisdom and goodness will bestow the merit of the Masses offered on other suffering souls.
Prayer: O Lord Jesus Christ, Who didst institute the unbloody Sacrifice of the Mass in commemoration of Thy Sacrifice upon the cross, we beseech Thee, bestow the merits of this Holy Sacrifice upon the souls in Purgatory, that they may soon be released from their pains. Who livest and reignest, world without end. Amen.
Special Intercession: Pray for the souls who were most zealous to assist at Mass.
Lord grant them eternal rest and let perpetual light shine upon them. May they rest in peace. Amen. (Three times.)
Practice: Assist at Mass for the relief of the suffering souls.
Invocation: My Jesus, mercy!