Summa Theologica, by St. Thomas Aquinas, [1947], at sacred-texts.com
We must now consider the effect of this sacrament: under which head there are three points of inquiry:
(1) Whether Extreme Unction avails for the remission of sins?
(2) Whether bodily health is an effect of this sacrament?
(3) Whether this sacrament imprints a character?
Objection 1: It would seem that Extreme Unction does not avail for the remission of sins. For when a thing can be attained by one means, no other is needed. Now repentance is required in the recipient of Extreme Unction for the remission of his sins. Therefore sins are not remitted by Extreme Unction.
Objection 2: Further, there are no more than three things in sin, the stain, the debt of punishment, and the remnants of sin. Now Extreme Unction does not remit the stain without contrition, and this remits sin even without Unction; nor does it remit the punishment, for if the recipient recover, he is still bound to fulfill the satisfaction enjoined; nor does it take away the remnants of sin, since the dispositions remaining from preceding acts still remain, as may easily be seen after recovery. Therefore remission of sins is by no means the effect of Extreme Unction.
Objection 3: Further, remission of sins takes place, not successively, but instantaneously. On the other hand, Extreme Unction is not done all at once, since several anointings are required. Therefore the remission of sins is not its effect.
On the contrary, It is written (James 5:15): "If he be in sins, they shall be forgiven him."
Further, every sacrament of the New Law confers grace. Now grace effects the forgiveness of sins. Therefore since Extreme Unction is a sacrament of the New Law, its effect is the remission of sins.
I answer that, Each sacrament was instituted for the purpose of one principal effect, though it may, in consequence, produce other effects besides. And since a sacrament causes what it signifies, the principal effect of a sacrament must be gathered from its signification. Now this sacrament is conferred by way of a kind of medicament, even as Baptism is conferred by way of washing, and the purpose of a medicament is to expel sickness. Hence the chief object of the institution of this sacrament is to cure the sickness of sin. Therefore, just as Baptism is a spiritual regeneration, and Penance, a spiritual resurrection, so Extreme Unction is a spiritual healing or cure. Now just as a bodily cure presupposes bodily life in the one who is cured, so does a spiritual cure presuppose spiritual life. Hence this sacrament is not an antidote to those defects which deprive man of spiritual life, namely. original and mortal sin, but is a remedy for such defects as weaken man spiritually, so as to deprive him of perfect vigor for acts of the life of grace or of glory; which defects consist in nothing else but a certain weakness and unfitness, the result in us of actual or original sin. against which weakness man is strengthened by this sacrament. Since, however, this strength is given by grace, which is incompatible with sin, it follows that. in consequence, if it finds any sin, either mortal or venial, it removes it as far as the guilt is concerned, provided there be no obstacle on the part of the recipient; just as we have stated to be the case with regard to the Eucharist and Confirmation (TP, Q[73], A[7]; TP, Q[79], A[3]). Hence, too, James speaks of the remission of sin as being conditional, for he says: "If he be in sins, they shall be forgiven him," viz. as to the guilt. Because it does not always blot out sin, since it does not always find any: but it always remits in respect of the aforesaid weakness which some call the remnants of sin. Some, however, maintain that it is instituted chiefly as a remedy for venial sin which cannot be cured perfectly in this lifetime: for which reason the sacrament of the dying is ordained specially against venial sin. But this does not seem to be true, since Penance also blots out venial sins sufficiently during this life as to their guilt, and that we cannot avoid them after doing penance, does not cancel the effect of the previous penance; moreover this is part of the weakness mentioned above.
Consequently we must say that the principal effect of this sacrament is the remission of sin, as to its remnants, and, consequently, even as to its guilt, if it find it.
Reply to Objection 1: Although the principal effect of a sacrament can be obtained without actually receiving that sacrament (either without any sacrament at all, or indirectly by means of some other sacrament), yet it never can be obtained without the purpose of receiving that sacrament. And so, since Penance was instituted chiefly against actual sin, whichever other sacrament may blot out sin indirectly, it does not exclude the necessity of Penance.
Reply to Objection 2: Extreme Unction remits sin in some way as to those three things. For, although the stain of sin is not washed out without contrition, yet this sacrament, by the grace which it bestows, makes the movement of the free will towards sin to be one of contrition, just as may occur in the Eucharist and Confirmation. Again it diminishes the debt of temporal punishment; and this indirectly, in as much as it takes away weakness, for a strong man bears the same punishment more easily than a weak man. Hence it does not follow that the measure of satisfaction is diminished. As to the remnants of sin, they do not mean here those dispositions which result from acts, and are inchoate habits so to speak, but a certain spiritual debility in the mind, which debility being removed, though such like habits or dispositions remain, the mind is not so easily prone to sin.
Reply to Objection 3: When many actions are ordained to one effect, the last is formal with respect to all the others that precede, and acts by virtue of them: wherefore by the last anointing is infused grace which gives the sacrament its effect.
Objection 1: It would seem that bodily health is not an effect of this sacrament. For every sacrament is a spiritual remedy. Now a spiritual remedy is ordained to spiritual health, just as a bodily remedy is ordained to health of the body. Therefore bodily health is not an effect of this sacrament.
Objection 2: Further, the sacraments always produce their effect in those who approach them in the proper dispositions. Now sometimes the recipient of this sacrament does not receive bodily health, no matter how devoutly he receives it. Therefore bodily health is not its effect.
Objection 3: Further, the efficacy of this sacrament is notified to us in the fifth chapter of James. Now healing is ascribed there as the effect, not of the anointing, but of the prayer, for he says: "The prayer of faith shall save the sick man." Therefore bodily healing is not an effect of this sacrament.
On the contrary, The operation of the Church is more efficacious since Christ's Passion than before. Now, before the Passion, those whom the apostles anointed with oil were healed (Mk. 6:13). Therefore unction has its effect now in healing bodies.
Further, the sacraments produce their effect by signifying it. Now Baptism signifies and effects a spiritual washing, through the bodily washing in which it consists outwardly. Therefore Extreme Unction signifies and causes a spiritual healing through the bodily healing which it effects externally.
I answer that, Just as Baptism causes a spiritual cleansing from spiritual stains by means of a bodily washing, so this sacrament causes an inward healing by means of an outward sacramental healing: and even as the baptismal washing has the effect of a bodily washing, since it effects even a bodily cleansing, so too, Extreme Unction has the effect of a bodily remedy, namely a healing of the body. But there is a difference, for as much as the bodily washing causes a bodily cleansing by a natural property of the bodily element, and consequently always causes it, whereas Extreme Unction causes a bodily healing, not by a natural property of the matter, but by the Divine power which works reasonably. And since reasonable working never produces a secondary effect, except in so far as it is required for the principal effect, it follows that a bodily healing does not always ensue from this sacrament, but only when it is requisite for the spiritual healing: and then it produces it always, provided there be no obstacle on the part of the recipient.
Reply to Objection 1: This objection proves that bodily health is not the principal effect of this sacrament: and this is true.
The Reply to the Second Objection is clear from what has been said above (cf. Q[29], A[8]).
Reply to Objection 3: This prayer is the form of this sacrament as stated above (Q[29], AA[8],9). Hence, so far as its form is concerned, this sacrament derives from it its efficacy in healing the body.
Objection 1: It would seem that this sacrament imprints a character. For a character is a distinctive sign. Now just as one who is baptized is distinguished from one who is not so is one who is anointed, from one who is not. Therefore, just as Baptism imprints a character so does Extreme Unction.
Objection 2: Further, there is an anointing in the sacraments or order and Confirmation, as there is in this sacrament. But a character is imprinted in those sacraments. Therefore a character is imprinted in this one also.
Objection 3: Further, every sacrament contains something that is a reality only, something that is a sacrament only, and something that is both reality and sacrament. Now nothing in this sacrament can be assigned as both reality and sacrament except a character. Therefore in this sacrament also, a character is imprinted.
On the contrary, No sacrament that imprints a character is repeated. But this sacrament is repeated as we shall state further on (Q[33]). Therefore it does not imprint a character.
Further, a sacramental character causes a distinction among those who are in the present Church. But Extreme Unction is given to one who is departing from the present Church. Therefore it does not imprint a character.
I answer that, A character is not imprinted except in those sacraments whereby man is deputed to some sacred duty. Now this sacrament is for no other purpose than a remedy, and man is not deputed thereby to do or receive anything holy. Therefore it does not imprint a character.
Reply to Objection 1: A character marks a distinction of . states with regard to duties which have to be performed in the Church, a distinction which a man does not receive by being anointed.
Reply to Objection 2: The unction of orders and Confirmation, is the unction of consecration whereby a man is deputed to some sacred duty, whereas this unction is remedial. Hence the comparison fails.
Reply to Objection 3: In this sacrament, that which is both reality and sacrament is not a character, but a certain inward devotion which is a kind of spiritual anointing.