The Passion of Jesus Christ and His Precious Blood shed for our salvation are an inexhaustible ocean of merit and satisfaction. It is by virtue of that Passion that we obtain all gifts and mercies from God. The mere commemoration which we make of it by way of prayer, when we offer to God the Blood of His only-begotten Son… has great power with God. […] If such be the value of an offering commemorative of the Passion, what must be said of the sacrifice of the Mass, which is the actual renewal of that same Passion?
—from Purgatory: Explained by the Lives and Legends of the Saints by Fr. F.X. Schouppe, S.J., Part Second: Purgatory, The Mystery of God’s Mercy – Ch. 17