I answer that, Two things may be considered in this sacrament, to wit, the sacrament itself, and the reality of the sacrament: and it appears from both that this sacrament has the power of forgiving venial sins. For this sacrament is received under the form of nourishing food. Now nourishment from food is requisite for the body to make good the daily waste caused by the action of natural heat. But something is also lost daily of our spirituality from the heat of concupiscence through venial sins, which lessen the fervor of charity, as was shown in the SS, Q[24], A[10]. And therefore it belongs to this sacrament to forgive venial sins. Hence Ambrose says (De Sacram. v) that this daily bread is taken "as a remedy against daily infirmity."
The reality of this sacrament is charity, not only as to its habit, but also as to its act, which is kindled in this sacrament; and by this means venial sins are forgiven. Consequently, it is manifest that venial sins are forgiven by the power of this sacrament.
Reply to Objection 1: Venial sins, although not opposed to the habit of charity, are nevertheless opposed to the fervor of its act, which act is kindled by this sacrament; by reason of which act venial sins are blotted out.
Reply to Objection 1: The passage quoted is not to be understood as if a man could not at some time be without all guilt of venial sin: but that the just do not pass through this life without committing venial sins.
Reply to Objection 3: The power of charity, to which this sacrament belongs, is greater than that of venial sins: because charity by its act takes away venial sins, which nevertheless cannot entirely hinder the act of charity. And the same holds good of this sacrament.
Whether the entire punishment due to sin is forgiven through this sacrament?
Objection 1: It seems that the entire punishment due to sin is forgiven through this sacrament. For through this sacrament man receives the effect of Christ's Passion within himself as stated above (AA[1],2), just as he does through Baptism. But through Baptism man receives forgiveness of all punishment, through the virtue of Christ's Passion, which satisfied sufficiently for all sins, as was explained above (Q[69], A[2] ). Therefore it seems the whole debt of punishment is forgiven through this sacrament.
Objection 2: Further, Pope Alexander I says (Ep. ad omnes orth.): "No sacrifice can be greater than the body and the blood of Christ." But man satisfied for his sins by the sacrifices of the old Law: for it is written ( Lev. 4:0 , Lev. 5:0 ): "If a man shall sin, let him offer" (so and so) "for his sin, and it shall be forgiven him." Therefore this sacrament avails much more for the forgiveness of all punishment.
Objection 3: Further, it is certain that some part of the debt of punishment is forgiven by this sacrament; for which reason it is sometimes enjoined upon a man, by way of satisfaction, to have masses said for himself. But if one part of the punishment is forgiven, for the same reason is the other forgiven: owing to Christ's infinite power contained in this sacrament. Consequently, it seems that the whole punishment can be taken away by this sacrament.
On the contrary, In that case no other punishment would have to be enjoined; just as none is imposed upon the newly baptized.
I answer that, This sacrament is both a sacrifice and a sacrament. it has the nature of a sacrifice inasmuch as it is offered up; and it has the nature of a sacrament inasmuch as it is received. And therefore it has the effect of a sacrament in the recipient, and the effect of a sacrifice in the offerer, or in them for whom it is offered.
If, then, it be considered as a sacrament, it produces its effect in two ways: first of all directly through the power of the sacrament; secondly as by a kind of concomitance, as was said above regarding what is contained in the sacrament (Q[76], AA[1],2). Through the power of the sacrament it produces directly that effect for which it was instituted. Now it was instituted not for satisfaction, but for nourishing spiritually through union between Christ and His members, as nourishment is united with the person nourished. But because this union is the effect of charity, from the fervor of which man obtains forgiveness, not only of guilt but also of punishment, hence it is that as a consequence, and by concomitance with the chief effect, man obtains forgiveness of the punishment, not indeed of the entire punishment, but according to the measure of his devotion and fervor.
But in so far as it is a sacrifice, it has a satisfactory power. Yet in satisfaction, the affection of the offerer is weighed rather than the quantity of the offering. Hence our Lord says ( Mk. 12:43 : cf. Lk. 21:4 ) of the widow who offered "two mites" that she "cast in more than all." Therefore, although this offering suffices of its own quantity to satisfy for all punishment, yet it becomes satisfactory for them for whom it is offered, or even for the offerers, according to the measure of their devotion, and not for the whole punishment.
Reply to Objection 1: The sacrament of Baptism is directly ordained for the remission of punishment and guilt: not so the Eucharist, because Baptism is given to man as dying with Christ, whereas the Eucharist is given as by way of nourishing and perfecting him through Christ. Consequently there is no parallel.
Reply to Objection 2: Those other sacrifices and oblations did not effect the forgiveness of the whole punishment, neither as to the quantity of the thing offered, as this sacrament does, nor as to personal devotion; from which it comes to pass that even here the whole punishment is not taken away.
Reply to Objection 3: If part of the punishment and not the whole be taken away by this sacrament, it is due to a defect not on the part of Christ's power, but on the part of man's devotion.
Whether man is preserved by this sacrament from future sins?
Objection 1: It seems that man is not preserved by this sacrament from future sins. For there are many that receive this sacrament worthily, who afterwards fall into sin. Now this would not happen if this sacrament were to preserve them from future sins. Consequently, it is not an effect of this sacrament to preserve from future sins.
Objection 2: Further, the Eucharist is the sacrament of charity, as stated above (A[4]). But charity does not seem to preserve from future sins, because it can be lost through sin after one has possessed it, as was stated in the SS, Q[24], A[11]. Therefore it seems that this sacrament does not preserve man from sin.
Objection 3: Further, the origin of sin within us is "the law of sin, which is in our members," as declared by the Apostle ( Rom. 7:23 ). But the lessening of the fomes, which is the law of sin, is set down as an effect not of this sacrament, but rather of Baptism. Therefore preservation from sin is not an effect of this sacrament.
On the contrary, our Lord said ( Jn. 6:50 ): "This is the bread which cometh down from heaven; that if any man eat of it, he may not die": which manifestly is not to be understood of the death of the body. Therefore it is to be understood that this sacrament preserves from spiritual death, which is through sin.
I answer that, Sin is the spiritual death of the soul. Hence man is preserved from future sin in the same way as the body is preserved from future death of the body: and this happens in two ways. First of all, in so far as man's nature is strengthened inwardly against inner decay, and so by means of food and medicine he is preserved from death. Secondly, by being guarded against outward assaults; and thus he is protected by means of arms by which he defends his body.
Now this sacrament preserves man from sin in both of these ways. For, first of all, by uniting man with Christ through grace, it strengthens his spiritual life, as spiritual food and spiritual medicine, according to Ps. 103:5 : "(That) bread strengthens [Vulg.: 'may strengthen'] man's heart." Augustine likewise says (Tract. xxvi in Joan.): "Approach without fear; it is bread, not poison." Secondly, inasmuch as it is a sign of Christ's Passion, whereby the devils are conquered, it repels all the assaults of demons. Hence Chrysostom says (Hom. xlvi in Joan.): "Like lions breathing forth fire, thus do we depart from that table, being made terrible to the devil."
Reply to Objection 1: The effect of this sacrament is received according to man's condition: such is the case with every active cause in that its effect is received in matter according to the condition of the matter. But such is the condition of man on earth that his free-will can be bent to good or evil. Hence, although this sacrament of itself has the power of preserving from sin, yet it does not take away from man the possibility of sinning.
Reply to Objection 2: Even charity of itself keeps man from sin, according to Rom. 13:10 : "The love of our neighbor worketh no evil": but it is due to the mutability of free-will that a man sins after possessing charity, just as after receiving this sacrament.