Article 3. Whether justice is a virtue?

Gregory says (Moral. ii, 49) that "the entire structure of good works is built on four virtues," viz. temperance, prudence, fortitude and justice.

A human virtue is one "which renders a human act and man himself good" [Ethic. ii, 6, and this can be applied to justice. For a man's act is made good through attaining the rule of reason, which is the rule whereby human acts are regulated. Hence, since justice regulates human operations, it is evident that it renders man's operations good, and, as Tully declares (De Officiis i, 7), good men are so called chiefly from their justice, wherefore, as he says again (De Officiis i, 7) "the luster of virtue appears above all in justice."

http://www.newadvent.org/summa/3058.htm#article3

Ave Maria!

Let's ask St. Joseph, who is called a just man in Matthew 1:19, to help us practice the virtue of justice!