76 Now the Apostle of the Gentiles proclaims the copious plenitude and the perfection of the sacrifice of the cross, when he says that Christ by one oblation has perfected for ever them that are sanctified. For the merits of this sacrifice, since they are altogether boundless and immeasurable, know no limits; for they are meant for all men of every time and place. This follows from the fact that in this sacrifice the God-Man is the priest and victim; that His immolation was entirely perfect, as was His obedience to the will of His eternal Father; and also that He suffered death as the Head of the human race: "See how we were bought: Christ hangs upon the cross, see at what a price He makes His purchase . . . He sheds His blood, He buys with His blood, He buys with the blood of the Spotless Lamb, He buys with the blood of God's only Son. He who buys is Christ; the price is His blood; the possession bought is the world."
Source: Mediator Dei (Vatican.va)