Objection 1. It seems that fortitude excels among all other virtues. For Ambrose says (De Offic. i): "Fortitude is higher, so to speak, than the rest."
Objection 2. Further, virtue is about that which is difficult and good. But fortitude is about most difficult things. Therefore it is the greatest of the virtues.
Objection 3. Further, the person of a man is more excellent than his possessions. But fortitude is about a man's person, for it is this that a man exposes to the danger of death for the good of virtue: whereas justice and the other moral virtues are about other and external things. Therefore fortitude is the chief of the moral virtues.
Objection 4.On the contrary, Tully says (De Offic. i): "Justice is the most resplendent of the virtues and gives its name to a good man."
Objection 5. Further, the Philosopher says (Rhet. i, 19): "Those virtues must needs be greatest which are most profitable to others." Now liberality seems to be more useful than fortitude. Therefore it is a greater virtue.
I answer that, As Augustine says (De Trin. vi), "In things that are great, but not in bulk, to be great is to be good": wherefore the better a virtue the greater it is. Now reason's good is man's good, according to Dionysius (Div. Nom. iv) prudence, since it is a perfection of reason, has the good essentially: while justice effects this good, since it belongs to justice to establish the order of reason in all human affairs: whereas the other virtues safeguard this good, inasmuch as they moderate the passions, lest they lead man away from reason's good. As to the order of the latter, fortitude holds the first place, because fear of dangers of death has the greatest power to make man recede from the good of reason: and after fortitude comes temperance, since also pleasures of touch excel all others in hindering the good of reason. Now to be a thing essentially ranks before effecting it, and the latter ranks before safeguarding it by removing obstacles thereto. Wherefore among the cardinal virtues, prudence ranks first, justice second, fortitude third, temperance fourth, and after these the other virtues.
Reply to Objection 1. Ambrose places fortitude before the other virtues, in respect of a certain general utility, inasmuch as it is useful both in warfare, and in matters relating to civil or home life. Hence he begins by saying (De Offic. i): "Now we come to treat of fortitude, which being higher so to speak than the others, is applicable both to warlike and to civil matters."
Reply to Objection 2. Virtue essentially regards the good rather than the difficult. Hence the greatness of a virtue is measured according to its goodness rather than its difficulty.
Reply to Objection 3. A man does not expose his person to dangers of death except in order to safeguard justice: wherefore the praise awarded to fortitude depends somewhat on justice. Hence Ambrose says (De Offic. i) that "fortitude without justice is an occasion of injustice; since the stronger a man is the more ready is he to oppress the weaker."
The Fourth argument is granted.
Reply to Objection 5. Liberality is useful in conferring certain particular favors: whereas a certain general utility attaches to fortitude, since it safeguards the whole order of justice. Hence the Philosopher says (Rhet. i, 9) that "just and brave men are most beloved, because they are most useful in war and peace."
Source: Summa Theologica (New Advent)