On The Holy Trinity by St. Augustine
Chapter 14.--Christ the Most Perfect Victim for Cleansing Our Faults. In Every Sacrifice Four Things are to Be Considered.
19. They do not understand, that not even the proudest of spirits themselves could rejoice in the honor of sacrifices, unless a true sacrifice was due to the one true God, in whose stead they desire to be worshipped: and that this cannot be rightly offered except by a holy and righteous priest; nor unless that which is offered be received from those for whom it is offered; and unless also it be without fault, so that it may be offered for cleansing the faulty. This at least all desire who wish sacrifice to be offered for themselves to God. Who then is so righteous and holy a priest as the only Son of God, who had no need to purge His own sins by sacrifice, neither original sins, nor those which are added by human life? And what could be so fitly chosen by men to be offered for them as human flesh? And what so fit for this immolation as mortal flesh? And what so clean for cleansing the faults of mortal men as the flesh born in and from the womb of a virgin, without any infection of carnal concupiscence? And what could be so acceptably offered and taken, as the flesh of our sacrifice, made the body of our priest? In such wise that, whereas four things are to be considered in every sacrifice, -- to whom it is offered, by whom it is offered, what is offered, for whom it is offered, -- the same One and true Mediator Himself, reconciling us to God by the sacrifice of peace, might remain one with Him to whom He offered, might make those one in Himself for whom He offered, Himself might be in one both the offerer and the offering.