1) Objection 1. It would seem that Christ’s Passion did not bring about our salvation by way of atonement. For it seems that to make the atonement devolves on him who commits the sin; as is clear in the other parts of penance, because he who has done the wrong must grieve over it and confess it. But Christ never sinned, according to 1 Pt. 2:22: “Who did no sin.” Therefore He made no atonement by His personal suffering.
Objection 2. Further, no atonement is made to another by committing a graver offense. But in Christ’s Passion the gravest of all offenses was perpetrated, because those who slew Him sinned most grievously, as stated above (47, 6). Consequently it seems that atonement could not be made to God by Christ’s Passion.
Objection 3. Further, atonement implies equality with the trespass, since it is an act of justice. But Christ’s Passion does not appear equal to all the sins of the human race, because Christ did not suffer in His Godhead, but in His flesh, according to 1 Pt. 4:1: “Christ therefore having suffered in the flesh.” Now the soul, which is the subject of sin, is of greater account than the flesh. Therefore Christ did not atone for our sins by His Passion.
On the contrary, It is written (Ps. 68:5) in Christ’s person: “Then did I pay that which I took not away.” But he has not paid who has not fully atoned. Therefore it appears that Christ by His suffering has fully atoned for our sins.
I answer that, He properly atones for an offense who offers something which the offended one loves equally, or even more than he detested the offense. But by suffering out of love and obedience, Christ gave more to God than was required to compensate for the offense of the whole human race. First of all, because of the exceeding charity from which He suffered; secondly, on account of the dignity of His life which He laid down in atonement, for it was the life of one who was God and man; thirdly, on account of the extent of the Passion, and the greatness of the grief endured, as stated above (46, 6). And therefore Christ’s Passion was not only a sufficient but a superabundant atonement for the sins of the human race; according to 1 John 2:2: “He is the propitiation for our sins: and not for ours only, but also for those of the whole world.”
Reply to Objection 1. The head and members are as one mystic person; and therefore Christ’s satisfaction belongs to all the faithful as being His members. Also, in so far as any two men are one in charity, the one can atone for the other as shall be shown later (XP, 13, 2). But the same reason does not hold good of confession and contrition, because atonement consists in an outward action, for which helps may be used, among which friends are to be computed.
Reply to Objection 2. Christ’s love was greater than His slayers’ malice: and therefore the value of His Passion in atoning surpassed the murderous guilt of those who crucified Him: so much so that Christ’s suffering was sufficient and superabundant atonement for His murderer’s crime.
Reply to Objection 3. The dignity of Christ’s flesh is not to be estimated solely from the nature of flesh, but also from the Person assuming it–namely, inasmuch as it was God’s flesh, the result of which was that it was of infinite worth. Summa Theologica, Part 3, Q 48.2.
2) Whether men were freed from the punishment of sin through Christ’s Passion?
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 Rm. 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 (Is. 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 Rm. 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 Pt. 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 (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 (Rm. 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.” Summa Theologica, Part 3, Q 49.3 .
Summa Contra Gentiles
1) Book 4, Chapt 53:
 But, again, let one say that it was necessary for the cleansing of our sins that Christ undergo death and the other seemingly abject things; as the Apostle says: “He was delivered up for our sins” (Rom. 4:25); and again: “He was offered once to exhaust the sins of many” (Heb. 9:28). This, too, seems awkward, because, in the first place, only by God’s grace are men cleansed of sins. Summa Contra Gentiles, 4.53.20.
 If Christ, moreover, had to die for the sins of men, since men sin frequently He should have had to undergo death frequently. Summa Contra Gentiles, 4.53.24.
 Now, let one say that it was especially because of original sin that Christ had to be born and to suffer, and that sin had infected the whole human race when the first man sinned. But this seems impossible. For, if other men are not equal to satisfying for original sin, neither does the death of Christ seem to have been satisfactory for the sins of the human race, since He Himself died in His human, not in His divine, nature. Summa Contra Gentiles, 4.53.25.
 Furthermore, if Christ made satisfaction enough for the sins of the human race, it seems unjust that men still suffer the penalties which were brought in, Scripture says, by sin. Summa Contra Gentiles, 4.53.26.[For rebuttal of this, see Summa Contra Gentiles 4.55.29 below.]
2) Book 4, Chapt 54:
 The tradition of the Church, moreover, teaches us that the whole human race was infected by sin. But the order of divine justice–as is clear from the foregoing–requires that God should not remit sin without satisfaction. But to satisfy for the sin of the whole human race was beyond the power of any pure man, because any pure man is something less than the whole human race in its entirety. Therefore, in order to free the human race from its common sin, someone had to satisfy who was both man and so proportioned to the satisfaction, and something above man that the merit might be enough to satisfy for the sin of the whole human race. But there is no greater than man in the order of beatitude, except God, for angels, although superior to man in the condition of nature, are not superior in the order of end, because the same end beatifies them. Therefore, it was necessary for man’s achievement of beatitude that God should become man to take away the sin of the human race. And this is what John the Baptist said of Christ: “Behold the Lamb of God, behold Him who takes away the sin of the world” (John 1:79). And the Apostle says: “As by the offense of one, unto all men to condemnation; so also by the justice of one, unto all men to justification” (Rom. 5:16). Summa Contra Gentiles 4.54.9.
3) Book 4, Chapt 55:
 This, too, is clear from what has been said: Christ had to suffer death not only to give an example of holding death in contempt out of love of the truth, but also to wash away the sins of others. This indeed took place when He who was without sin willed to suffer the penalty due to sin that He might take on Himself the penalty due to others, and make satisfaction for others. And although the grace of God suffices by itself for the remission of sins, as the nineteenth argument was proposing, nonetheless in the remission of sin something is required on the part of him whose sin is remitted: namely, that he satisfy the one offended. And since other men were unable to do this for themselves, Christ did this for all by suffering a voluntary death out of charity. Summa Contra Gentiles, 4.55.22.
 Be it granted, also, that in the punishment of sins he who sinned ought to be punished, as the twentieth argument was proposing; for all that, in the matter of satisfaction one can bear another’s penalty. For, when penalty is inflicted for sin, we weigh his iniquity who is punished; in satisfaction, however, when to placate the one offended, some other voluntarily assumes the penalty, we consider the charity and benevolence of him who makes satisfaction, and this most especially appears when one assumes the penalty of another. And, therefore, God does receive from one satisfaction for another, as was shown in Book III. Summa Contra Gentiles, 4.55.23.
 But to satisfy for the whole human race (this was shown previously) was beyond the power of any mere man; neither was an angel equal to this, as the twenty-first argument was proceeding. For, granted an angel in some natural properties has a power beyond man’s, nonetheless in the sharing of beatitude (and by the satisfaction man was to be restored to this) the angel is man’s equal. And again, there would be no full restoration of man’s dignity if man were rendered obnoxious to the angel satisfying for man. Summa Contra Gentiles, 4.55.24.
 One should, of course, know that the death of Christ had its satisfying power from His charity in which He bore death voluntarily, and not from the iniquity of His killers who sinned in killing Him; because sin is not wiped out by sin, as the twenty-second argument proposed. Summa Contra Gentiles, 4.55.25.
 And although the death of Christ was satisfactory for sin, it was unnecessary for Him to die just as many times as men sinned, as the twenty-third argument was concluding. The death of Christ was sufficient for the expiation of all sins; and this by reason of the extraordinary charity in which He bore death, as well as by reason of the dignity of the satisfying person who was God and man. But even in human affairs it is clear that by as much as the person is higher, by so much is the penalty he bears reckoned for more, whether reckoned by the humility and charity of the one suffering or by the fault of the one incurring the penalty. Summa Contra Gentiles, 4.55.26.
 Of course, for the satisfaction of the sin of the entire human race the death of Christ was sufficient. For, although He died only in His human nature, as the twenty-fourth argument was proposing, the dignity of the person suffering and this is the Person of the Son of God-renders His death precious. For, as was said above, just as it is a greater crime to commit an injury to a person who stands out more in dignity, so it is more virtuous and proceeds from greater charity that the greater person submit Himself voluntarily to suffering for others. Summa Contra Gentiles, 4.55.27.
 But, although Christ has by His death satisfied sufficiently for original sin, there is nothing awkward in this: that the penalties consequent on original sin still remain in all, even in those who are given a share in Christ’s redemption, as the twenty-fifth argument was proceeding. For it was both fitting and useful to have the penalty remain even when the fault was taken away. First, indeed, to achieve conformity of the faithful to Christ as members to the head; hence, just as Christ first bore many sufferings, and thus arrived at the glory of immortality, it also was becoming to His faithful first to undergo sufferings and so to arrive at immortality, bearing in themselves, so to say, the marks of the passion of Christ, in order to achieve a likeness to His glory. So the Apostle says: “Heirs, indeed of God, and joint-heirs with Christ: yet so, if we suffer with Him, that we may be also glorified with Him” (Rom. 8:17). Second, because, if men coming to Jesus were forthwith to achieve immortality and impassibility, many men would approach Christ more for these bodily benefits than for spiritual goods. And this is against the intention of Christ who came into the world to change men from love of bodily things to love of spiritual things. Third, because, if those who come to Christ were forthwith rendered incapable of suffering and death, this would somehow compel men to accept faith in Christ. And thus the merit of faith would be diminished. Summa Contra Gentiles, 4.55.28.
 Granted, of course, that Christ has sufficiently satisfied for the sins of the human race by His death, as the twenty-sixth argument proposed, every single one, for all that, must seek the remedies of his own salvation. For the death of Christ is, so to say, a kind of universal cause of salvation, as the sin of the first man was a kind of universal cause of damnation. But a universal cause must be applied specially to each one, that he may receive the effect of the universal cause. The effect, then, of the sin of the first parent comes to each one in the origin of the flesh, but the effect of the death of Christ comes to each one in a spiritual regeneration in which the man is somehow conjoined with Christ and incorporated into Him. And for this reason each must seek to be regenerated through Christ, and must himself undertake to do those things in which the power of Christ’s death operates. Summa Contra Gentiles, 4.55.29.
 Thus, then, from what has been set down it is to some extent clear that what the Catholic faith preaches about the Incarnation contains nothing impossible and nothing inharmonious. Summa Contra Gentiles, 4.55.31.
On Reasons for Our Faith
1) But it must further be noticed that satisfaction is also measured in accord with the dignity of him who satisfies. For one word of apology by a king offered in satisfaction for some injury is considered greater than if anyone else should either kneel, or prostrate naked, or undertake any humiliation to satisfy someone injured. No mere man, however, had that infinite dignity such that his satisfaction could be reputed worthy in respect to the injury done God. Hence, it was necessary that some man of infinite dignity be found who would undergo punishment for all and so satisfy fully for the sins of the whole world. For this, then, the only-begotten Word of God, true God and Son of God, assumed a human nature and willed to suffer death in it that satisfying He might cleanse the entire human race of sin. Hence, St. Peter also says, “Christ died once for our sins the Just for the unjust, that He might offer us to God” (1 Pet 3: 18). Thomas Aquinas, On Reasons for Our Faith Against the Muslims, and a Reply to the Denial of Purgatory by Certain Greeks and Armenians: To the Cantor of Antioch, trans. Peter Damian M. Fehlner (New Bedford, MA: Franscicans of the Immaculate, 2002), 52-53.
Literal Exposition on Job
1) And here one should consider that man, who had been constituted immortal by God, incurred death through sin, according to the text of Romans 5:12: “Through one man sin entered into this world, and through sin, death,” and from this sin, of course, the human race had to be redeemed through Christ, a redemption which Job foresaw through the spirit of faith. Now Christ redeemed us from sin through death by dying for us. He did not due, however, in such a way that death engulfed him since, although he died in humanity, he nevertheless could not die in his divinity. Thomas Aquinas, The Literal Exposition on Job, trans. Anthony Damico (Altanta, Georgia: Scholars Press, 1989), 269.
Classic secondary source: David Paraeus:
1) Thomas writes: “The merit of Christ, as to its sufficiency, extends equally to all, but not as to its efficacy, which happens partly on account of free will, and partly on account of the election of God, through which the effects of the merits of Christ are mercifully bestowed upon some, and withheld from others according to the just judgment of God.”
2) Thomas on the 5. Of the Apoc. writes on this manner.
Of the redemption purchased by the passion of Christ we may speak in a double sense & signification, either respecting the sufficiency thereof; & so his passion redeemed all because as concerning himself he delivered all.