Objection 1. It would seem that men were not freed from the punishment of sin by Christ's Passion. For the chief punishment of sin is eternal damnation. But those damned in hell for their sins were not set free by Christ's Passion, because "in hell there is no redemption" [Office of the Dead, Resp. vii]. It seems, therefore, that Christ's Passion did not deliver men from the punishment of sin.
Objection 2. Further, no punishment should be imposed upon them who are delivered from the debt of punishment. But a satisfactory punishment is imposed upon penitents. Consequently, men were not freed from the debt of punishment by Christ's Passion.
Objection 3. Further, death is a punishment of sin, according to Romans 6:23: "The wages of sin is death." But men still die after Christ's Passion. Therefore it seems that we have not been delivered from the debt of punishment.
On the contrary, It is written (Isaiah 53:4): "Surely He hath borne our iniquities and carried our sorrows."
I answer that, Through Christ's Passion we have been delivered from the debt of punishment in two ways. First of all, directly--namely, inasmuch as Christ's Passion was sufficient and superabundant satisfaction for the sins of the whole human race: but when sufficient satisfaction has been paid, then the debt of punishment is abolished. In another way--indirectly, that is to say--in so far as Christ's Passion is the cause of the forgiveness of sin, upon which the debt of punishment rests.
Reply to Objection 1. Christ's Passion works its effect in them to whom it is applied, through faith and charity and the sacraments of faith. And, consequently, the lost in hell cannot avail themselves of its effects, since they are not united to Christ in the aforesaid manner.
Reply to Objection 2. As stated above (1, ad 4,5), in order to secure the effects of Christ's Passion, we must be likened unto Him. Now we are likened unto Him sacramentally in Baptism, according to Romans 6:4: "For we are buried together with Him by baptism into death." Hence no punishment of satisfaction is imposed upon men at their baptism, since they are fully delivered by Christ's satisfaction. But because, as it is written (1 Peter 3:18), "Christ died" but "once for our sins," therefore a man cannot a second time be likened unto Christ's death by the sacrament of Baptism. Hence it is necessary that those who sin after Baptism be likened unto Christ suffering by some form of punishment or suffering which they endure in their own person; yet, by the co-operation of Christ's satisfaction, much lighter penalty suffices than one that is proportionate to the sin.
Reply to Objection 3. Christ's satisfaction works its effect in us inasmuch as we are incorporated with Him, as the members with their head, as stated above (Article 1). Now the members must be conformed to their head. Consequently, as Christ first had grace in His soul with bodily passibility, and through the Passion attained to the glory of immortality, so we likewise, who are His members, are freed by His Passion from all debt of punishment, yet so that we first receive in our souls "the spirit of adoption of sons," whereby our names are written down for the inheritance of immortal glory, while we yet have a passible and mortal body: but afterwards, "being made conformable" to the sufferings and death of Christ, we are brought into immortal glory, according to the saying of the Apostle (Romans 8:17): "And if sons, heirs also: heirs indeed of God, and joint heirs with Christ; yet so if we suffer with Him, that we may be also glorified with Him."
Source: Summa Theologica (New Advent)