Objection 1. It seems that it is possible to have patience without grace. For the more his reason inclines to a thing, the more is it possible for the rational creature to accomplish it. Now it is more reasonable to suffer evil for the sake of good than for the sake of evil. Yet some suffer evil for evil's sake, by their own virtue and without the help of grace; for Augustine says (De Patientia iii) that "men endure many toils and sorrows for the sake of the things they love sinfully." Much more, therefore, is it possible for man, without the help of grace, to bear evil for the sake of good, and this is to be truly patient.
Objection 2. Further, some who are not in a state of grace have more abhorrence for sinful evils than for bodily evils: hence some heathens are related to have endured many hardships rather than betray their country or commit some other misdeed. Now this is to be truly patient. Therefore it seems that it is possible to have patience without the help of grace.
Objection 3. Further, it is quite evident that some go through much trouble and pain in order to regain health of the body. Now the health of the soul is not less desirable than bodily health. Therefore in like manner one may, without the help of grace, endure many evils for the health of the soul, and this is to be truly patient.
On the contrary, It is written (Psalm 61:6): "From Him," i.e. from God, "is my patience."
I answer that, As Augustine says (De Patientia iv), "the strength of desire helps a man to bear toil and pain: and no one willingly undertakes to bear what is painful, save for the sake of that which gives pleasure." The reason of this is because sorrow and pain are of themselves displeasing to the soul, wherefore it would never choose to suffer them for their own sake, but only for the sake of an end. Hence it follows that the good for the sake of which one is willing to endure evils, is more desired and loved than the good the privation of which causes the sorrow that we bear patiently. Now the fact that a man prefers the good of grace to all natural goods, the loss of which may cause sorrow, is to be referred to charity, which loves God above all things. Hence it is evident that patience, as a virtue, is caused by charity, according to 1 Corinthians 13:4, "Charity is patient."
But it is manifest that it is impossible to have charity save through grace, according to Romans 5:5, "The charity of God is poured forth in our hearts by the Holy Ghost Who is given to us." Therefore it is clearly impossible to have patience without the help of grace.
Reply to Objection 1. The inclination of reason would prevail in human nature in the state of integrity. But in corrupt nature the inclination of concupiscence prevails, because it is dominant in man. Hence man is more prone to bear evils for the sake of goods in which the concupiscence delights here and now, than to endure evils for the sake of goods to come, which are desired in accordance with reason: and yet it is this that pertains to true patience.
Reply to Objection 2. The good of a social virtue [Cf. I-II, 61, 5] is commensurate with human nature; and consequently the human will can tend thereto without the help of sanctifying grace, yet not without the help of God's grace [Cf. I-II, 109, 2]. On the other hand, the good of grace is supernatural, wherefore man cannot tend thereto by a natural virtue. Hence the comparison fails.
Reply to Objection 3. Even the endurance of those evils which a man bears for the sake of his body's health, proceeds from the love a man naturally has for his own flesh. Hence there is no comparison between this endurance and patience which proceeds from a supernatural love.
Source: Summa Theologica (New Advent)