Objection 1. It would seem that contrition is not the greatest possible sorrow in the world. For sorrow is the sensation of hurt. But some hurts are more keenly felt than the hurt of sin, e.g. the hurt of a wound. Therefore contrition is not the greatest sorrow.
Objection 2. Further, we judge of a cause according to its effect. Now the effect of sorrow is tears. Since therefore sometimes a contrite person does not shed outward tears for his sins, whereas he weeps for the death of a friend, or for a blow, or the like, it seems that contrition is not the greatest sorrow.
Objection 3. Further, the more a thing is mingled with its contrary, the less its intensity. But the sorrow of contrition has a considerable admixture of joy, because the contrite man rejoices in his delivery, in the hope of pardon, and in many like things. Therefore his sorrow is very slight.
Objection 4. Further, the sorrow of contrition is a kind of displeasure. But there are many things more displeasing to the contrite than their past sins; for they would not prefer to suffer the pains of hell rather than to sin. nor to have suffered, nor yet to suffer all manner of temporal punishment; else few would be found contrite. Therefore the sorrow of contrition is not the greatest.
On the contrary, According to Augustine (De Civ. Dei xiv, 7, 9), "all sorrow is based on love." Now the love of charity, on which the sorrow of contrition is based, is the greatest love. Therefore the sorrow of contrition is the greatest sorrow.
Further, sorrow is for evil. Therefore the greater the evil, the greater the sorrow. But the fault is a greater evil than its punishment. Therefore contrition which is sorrow for fault, surpasses all other sorrow.
I answer that, As stated above (1, 2, ad 1), there is a twofold sorrow in contrition: one is in the will, and is the very essence of contrition, being nothing else than displeasure at past sin, and this sorrow, in contrition, surpasses all other sorrows. For the more pleasing a thing is, the more displeasing is its contrary. Now the last end is above all things pleasing: wherefore sin, which turns us away from the last end, should be, above all things, displeasing. The other sorrow is in the sensitive part, and is caused by the former sorrow either from natural necessity, in so far as the lower powers follow the movements of the higher, or from choice, in so far as a penitent excites in himself this sorrow for his sins. In neither of these ways is such sorrow, of necessity, the greatest, because the lower powers are more deeply moved by their own objects than through redundance from the higher powers. Wherefore the nearer the operation of the higher powers approaches to the objects of the lower powers, the more do the latter follow the movement of the former. Consequently there is greater pain in the sensitive part, on account of a sensible hurt, than that which redounds into the sensitive part from the reason; and likewise, that which redounds from the reason when it deliberates on corporeal things, is greater than that which redounds from the reason in considering spiritual things. Therefore the sorrow which results in the sensitive part from the reason's displeasure at sin, is not greater than the other sorrows of which that same part is the subject: and likewise, neither is the sorrow which is assumed voluntarily greater than other sorrows--both because the lower appetite does not obey the higher appetite infallibly, as though in the lower appetite there should arise a passion of such intensity and of such a kind as the higher appetite might ordain--and because the passions are employed by the reason, in acts of virtue, according to a certain measure, which the sorrow that is without virtue sometimes does not observe, but exceeds.
Reply to Objection 1. Just as sensible sorrow is on account of the sensation of hurt, so interior sorrow is on account of the thought of something hurtful. Therefore, although the hurt of sin is not perceived by the external sense, yet it is perceived to be the most grievous hurt by the interior sense or reason.
Reply to Objection 2. Affections of the body are the immediate result of the sensitive passions and, through them, of the emotions of the higher appetite. Hence it is that bodily tears flow more quickly from sensible sorrow, or even from a thing that hurts the senses, than from the spiritual sorrow of contrition.
Reply to Objection 3. The joy which a penitent has for his sorrow does not lessen his displeasure (for it is not contrary to it), but increases it, according as every operation is increased by the delight which it causes, as stated in Ethic. x, 5. Thus he who delights in learning a science, learns the better, and, in like manner, he who rejoices in his displeasure, is the more intensely displeased. But it may well happen that this joy tempers the sorrow that results from the reason in the sensitive part.
Reply to Objection 4. The degree of displeasure at a thing should be proportionate to the degree of its malice. Now the malice of mortal sin is measured from Him against Whom it is committed, inasmuch as it is offensive to Him; and from him who sins, inasmuch as it is hurtful to him. And, since man should love God more than himself, therefore he should hate sin, as an offense against God, more than as being hurtful to himself. Now it is hurtful to him chiefly because it separates him from God; and in this respect the separation from God which is a punishment, should be more displeasing than the sin itself, as causing this hurt (since what is hated on account of something else, is less hated), but less than the sin, as an offense against God. Again, among all the punishments of malice a certain order is observed according to the degree of the hurt. Consequently, since this is the greatest hurt, inasmuch as it consists in privation of the greatest good, the greatest of all punishments will be separation from God.
Again, with regard to this displeasure, it is necessary to observe that there is also an accidental degree of malice, in respect of the present and the past; since what is past, is no more, whence it has less of the character of malice or goodness. Hence it is that a man shrinks from suffering an evil at the present, or at some future time, more than he shudders at the past evil: wherefore also, no passion of the soul corresponds directly to the past, as sorrow corresponds to present evil, and fear to future evil. Consequently, of two past evils, the mind shrinks the more from that one which still produces a greater effect at the present time, or which, it fears, will produce a greater effect in the future, although in the past it was the lesser evil. And, since the effect of the past sin is sometimes not so keenly felt as the effect of the past punishment, both because sin is more perfectly remedied than punishment, and because bodily defect is more manifest than spiritual defect, therefore even a man, who is well disposed, sometimes feels a greater abhorrence of his past punishment than of his past sin, although he would be ready to suffer the same punishment over again rather than commit the same sin.
We must also observe, in comparing sin with punishment, that some punishments are inseparable from offense of God, e.g. separation from God; and some also are everlasting, e.g. the punishment of hell. Therefore the punishment to which is connected offense of God is to be shunned in the same way as sin; whereas that which is everlasting is simply to be shunned more than sin. If, however, we separate from these punishments the notion of offense, and consider only the notion of punishment, they have the character of malice, less than sin has as an offense against God: and for this reason should cause less displeasure.
We must, however, take note that, although the contrite should be thus disposed, yet he should not be questioned about his feelings, because man cannot easily measure them. Sometimes that which displeases least seems to displease most, through being more closely connected with some sensible hurt, which is more known to us.
Source: Summa Theologica (New Advent)