On the contrary, It is written (Apoc. 1:5): "He loved us, and washed us from our sins in His own blood."
I answer that, Christ's Passion is the proper cause of the forgiveness of sins in three ways. First of all, by way of exciting our charity, because, as the Apostle says (Rom. 5:8): "God commendeth His charity towards us: because when as yet we were sinners, according to the time, Christ died for us." But it is by charity that we procure pardon of our sins, according to Luke 7:47: "Many sins are forgiven her because she hath loved much." Secondly, Christ's Passion causes forgiveness of sins by way of redemption. For since He is our head, then, by the Passion which He endured from love and obedience, He delivered us as His members from our sins, as by the price of His Passion: in the same way as if a man by the good industry of his hands were to redeem himself from a sin committed with his feet. For, just as the natural body is one though made up of diverse members, so the whole Church, Christ's mystic body, is reckoned as one person with its head, which is Christ. Thirdly, by way of efficiency, inasmuch as Christ's flesh, wherein He endured the Passion, is the instrument of the Godhead, so that His sufferings and actions operate with Divine power for expelling sin.
Reply Obj. 1: Although Christ did not suffer as God, nevertheless His flesh is the instrument of the Godhead; and hence it is that His Passion has a kind of Divine Power of casting out sin, as was said above.
Reply Obj. 2: Although Christ's Passion is corporeal, still it derives a kind of spiritual energy from the Godhead, to which the flesh is united as an instrument: and according to this power Christ's Passion is the cause of the forgiveness of sins.
Reply Obj. 3: Christ by His Passion delivered us from our sins causally—that is, by setting up the cause of our deliverance, from which cause all sins whatsoever, past, present, or to come, could be forgiven: just as if a doctor were to prepare a medicine by which all sicknesses can be cured even in future.
Reply Obj. 4: As stated above, since Christ's Passion preceded, as a kind of universal cause of the forgiveness of sins, it needs to be applied to each individual for the cleansing of personal sins. Now this is done by baptism and penance and the other sacraments, which derive their power from Christ's Passion, as shall be shown later (Q. 62, A. 5).
Reply Obj. 5: Christ's Passion is applied to us even through faith, that we may share in its fruits, according to Rom. 3:25: "Whom God hath proposed to be a propitiation, through faith in His blood." But the faith through which we are cleansed from sin is not lifeless faith, which can exist even with sin, but faith living through charity; that thus Christ's Passion may be applied to us, not only as to our minds, but also as to our hearts. And even in this way sins are forgiven through the power of the Passion of Christ. _______________________
SECOND ARTICLE [III, Q. 49, Art. 2]
Whether We Were Delivered from the Devil's Power Through Christ's
Passion?
Objection 1: It would seem that we were not delivered from the power of the devil through Christ's Passion. For he has no power over others, who can do nothing to them without the sanction of another. But without the Divine permission the devil could never do hurt to any man, as is evident in the instance of Job (1, 2), where, by power received from God, the devil first injured him in his possessions, and afterwards in his body. In like manner it is stated (Matt. 8:31, 32) that the devils could not enter into the swine except with Christ's leave. Therefore the devil never had power over men: and hence we are not delivered from his power through Christ's Passion.