Objection 1. It seems that patience is the greatest of the virtues. For in every genus that which is perfect is the greatest. Now "patience hath a perfect work" (James 1:4). Therefore patience is the greatest of the virtues.
Objection 2. Further, all the virtues are directed to the good of the soul. Now this seems to belong chiefly to patience; for it is written (Luke 21:19): "In your patience you shall possess your souls." Therefore patience is the greatest of the virtues.
Objection 3. Further, seemingly that which is the safeguard and cause of other things is greater than they are. But according to Gregory (Hom. xxxv in Evang.) "patience is the root and safeguard of all the virtues." Therefore patience is the greatest of the virtues.
On the contrary, It is not reckoned among the four virtues which Gregory (Moral. xxii) and Augustine (De Morib. Eccl. xv) call principal.
I answer that, Virtues by their very nature are directed to good. For it is virtue that "makes its possessor good, and renders the latter's work good" (Ethic. ii, 6). Hence it follows that a virtue's superiority and preponderance over other virtues is the greater according as it inclines man to good more effectively and directly. Now those virtues which are effective of good, incline a man more directly to good than those which are a check on the things which lead man away from good: and just as among those that are effective of good, the greater is that which establishes man in a greater good (thus faith, hope, and charity are greater than prudence and justice); so too among those that are a check on things that withdraw man from good, the greater virtue is the one which is a check on a greater obstacle to good. But dangers of death, about which is fortitude, and pleasures of touch, with which temperance is concerned, withdraw man from good more than any kind of hardship, which is the object of patience. Therefore patience is not the greatest of the virtues, but falls short, not only of the theological virtues, and of prudence and justice which directly establish man in good, but also of fortitude and temperance which withdraw him from greater obstacles to good.
Reply to Objection 1. Patience is said to have a perfect work in bearing hardships: for these give rise first to sorrow, which is moderated by patience; secondly, to anger, which is moderated by meekness; thirdly, to hatred, which charity removes; fourthly, to unjust injury, which justice forbids. Now that which removes the principle is the most perfect.
Yet it does not follow, if patience be more perfect in this respect, that it is more perfect simply.
Reply to Objection 2. Possession denotes undisturbed ownership; wherefore man is said to possess his soul by patience, in so far as it removes by the root the passions that are evoked by hardships and disturb the soul.
Reply to Objection 3. Patience is said to be the root and safeguard of all the virtues, not as though it caused and preserved them directly, but merely because it removes their obstacles.
Source: Summa Theologica (New Advent)