From the Summa Theologica.
Whether the pain of Christ's Passion was greater than all other pains?
Objection 1. It would seem that the pain of Christ's Passion was not greater than all other pains. For the sufferer's pain is increased by the sharpness and the duration of the suffering. But some of the martyrs endured sharper and more prolonged pains than Christ, as is seen in St. Lawrence, who was roasted upon a gridiron; and in St. Vincent, whose flesh was torn with iron pincers. Therefore it seems that the pain of the suffering Christ was not the greatest.
Objection 2. Further, strength of soul mitigates pain, so much so that the Stoics held there was no sadness in the soul of a wise man; and Aristotle (Ethic. ii) holds that moral virtue fixes the mean in the passions. But Christ had most perfect strength of soul. Therefore it seems that the greatest pain did not exist in Christ.
Objection 3. Further, the more sensitive the sufferer is, the more acute will the pain be. But the soul is more sensitive than the body, since the body feels in virtue of the soul; also, Adam in the state of innocence seems to have had a body more sensitive than Christ had, who assumed a human body with its natural defects. Consequently, it seems that the pain of a sufferer in purgatory, or in hell, or even Adam's pain, if he suffered at all, was greater than Christ's in the Passion.
Objection 4. Further, the greater the good lost, the greater the pain. But by sinning the sinner loses a greater good than Christ did when suffering; since the life of grace is greater than the life of nature: also, Christ, who lost His life, but was to rise again after three days, seems to have lost less than those who lose their lives and abide in death. Therefore it seems that Christ's pain was not the greatest of all.
Objection 5. Further, the victim's innocence lessens the sting of his sufferings. But Christ died innocent, according to Jeremiah 9:19: "I was as a meek lamb, that is carried to be a victim." Therefore it seems that the pain of Christ's Passion was not the greatest.
Objection 6. Further, there was nothing superfluous in Christ's conduct. But the slightest pain would have sufficed to secure man's salvation, because from His Divine Person it would have had infinite virtue. Therefore it would have been superfluous to choose the greatest of all pains.
On the contrary, It is written (Lamentations 1:12) on behalf of Christ's Person: "O all ye that pass by the way attend, and see if there be any sorrow like unto My sorrow."
I answer that, As we have stated, when treating of the defects assumed by Christ (15, 5,6), there was true and sensible pain in the suffering Christ, which is caused by something hurtful to the body: also, there was internal pain, which is caused from the apprehension of something hurtful, and this is termed "sadness." And in Christ each of these was the greatest in this present life. This arose from four causes.
First of all, from the sources of His pain. For the cause of the sensitive pain was the wounding of His body; and this wounding had its bitterness, both from the extent of the suffering already mentioned (5]) and from the kind of suffering, since the death of the crucified is most bitter, because they are pierced in nervous and highly sensitive parts--to wit, the hands and feet; moreover, the weight of the suspended body intensifies the agony. And besides this there is the duration of the suffering because they do not die at once like those slain by the sword. The cause of the interior pain was, first of all, all the sins of the human race, for which He made satisfaction by suffering; hence He ascribes them, so to speak, to Himself, saying (Psalm 21:2): "The words of my sins."
Secondly, especially the fall of the Jews and of the others who sinned in His death chiefly of the apostles, who were scandalized at His Passion. Thirdly, the loss of His bodily life, which is naturally horrible to human nature.
The magnitude of His suffering may be considered, secondly, from the susceptibility of the sufferer as to both soul and body. For His body was endowed with a most perfect constitution, since it was fashioned miraculously by the operation of the Holy Ghost; just as some other things made by miracles are better than others, as Chrysostom says (Hom. xxii in Joan.) respecting the wine into which Christ changed the water at the wedding-feast. And, consequently, Christ's sense of touch, the sensitiveness of which is the reason for our feeling pain, was most acute. His soul likewise, from its interior powers, apprehended most vehemently all the causes of sadness.
Thirdly, the magnitude of Christ's suffering can be estimated from the singleness of His pain and sadness. In other sufferers the interior sadness is mitigated, and even the exterior suffering, from some consideration of reason, by some derivation or redundance from the higher powers into the lower; but it was not so with the suffering Christ, because "He permitted each one of His powers to exercise its proper function," as Damascene says (De Fide Orth. iii).
Fourthly, the magnitude of the pain of Christ's suffering can be reckoned by this, that the pain and sorrow were accepted voluntarily, to the end of men's deliverance from sin; and consequently He embraced the amount of pain proportionate to the magnitude of the fruit which resulted therefrom.
From all these causes weighed together, it follows that Christ's pain was the very greatest.
Reply to Objection 1. This argument follows from only one of the considerations adduced--namely, from the bodily injury, which is the cause of sensitive pain; but the torment of the suffering Christ is much more intensified from other causes, as above stated.
Reply to Objection 2. Moral virtue lessens interior sadness in one way, and outward sensitive pain in quite another; for it lessens interior sadness directly by fixing the mean, as being its proper matter, within limits. But, as was laid down in I-II, 64, 2, moral virtue fixes the mean in the passions, not according to mathematical quantity, but according to quantity of proportion, so that the passion shall not go beyond the rule of reason. And since the Stoics held all sadness to be unprofitable, they accordingly believed it to be altogether discordant with reason, and consequently to be shunned altogether by a wise man. But in very truth some sadness is praiseworthy, as Augustine proves (De Civ. Dei xiv)--namely, when it flows from holy love, as, for instance, when a man is saddened over his own or others' sins. Furthermore, it is employed as a useful means of satisfying for sins, according to the saying of the Apostle (2 Corinthians 7:10): "The sorrow that is according to God worketh penance, steadfast unto salvation." And so to atone for the sins of all men, Christ accepted sadness, the greatest in absolute quantity, yet not exceeding the rule of reason. But moral virtue does not lessen outward sensitive pain, because such pain is not subject to reason, but follows the nature of the body; yet it lessens it indirectly by redundance of the higher powers into the lower. But this did not happen in Christ's case, as stated above (cf. 14, 1, ad 2; 45, 2).
Reply to Objection 3. The pain of a suffering, separated soul belongs to the state of future condemnation, which exceeds every evil of this life, just as the glory of the saints surpasses every good of the present life. Accordingly, when we say that Christ's pain was the greatest, we make no comparison between His and the pain of a separated soul. But Adam's body could not suffer, except he sinned, so that he would become mortal, and passible. And, though actually suffering, it would have felt less pain than Christ's body, for the reasons already stated. From all this it is clear that even if by impassibility Adam had suffered in the state of innocence, his pain would have been less than Christ's.
Reply to Objection 4. Christ grieved not only over the loss of His own bodily life, but also over the sins of all others. And this grief in Christ surpassed all grief of every contrite heart, both because it flowed from a greater wisdom and charity, by which the pang of contrition is intensified, and because He grieved at the one time for all sins, according to Isaiah 53:4: "Surely He hath carried our sorrows." But such was the dignity of Christ's life in the body, especially on account of the Godhead united with it, that its loss, even for one hour, would be a matter of greater grief than the loss of another man's life for howsoever long a time. Hence the Philosopher says (Ethic. iii) that the man of virtue loves his life all the more in proportion as he knows it to be better; and yet he exposes it for virtue's sake. And in like fashion Christ laid down His most beloved life for the good of charity, according to Jeremiah 12:7: "I have given My dear soul into the hands of her enemies."
Reply to Objection 5. The sufferer's innocence does lessen numerically the pain of the suffering, since, when a guilty man suffers, he grieves not merely on account of the penalty, but also because of the crime. whereas the innocent man grieves only for the penalty: yet this pain is more intensified by reason of his innocence, in so far as he deems the hurt inflicted to be the more undeserved. Hence it is that even others are more deserving of blame if they do not compassionate him, according to Isaiah 57:1: "The just perisheth, and no man layeth it to heart."
Reply to Objection 6. Christ willed to deliver the human race from sins not merely by His power, but also according to justice. And therefore He did not simply weigh what great virtue His suffering would have from union with the Godhead, but also how much, according to His human nature, His pain would avail for so great a satisfaction.