See CCC §1805, 1834
A virtue is a habitual disposition to do good. Among all the virtues, there are four that play a pivotal role and accordingly are called cardinal.
Prudence – Justice – Fortitude – Temperance.
Prudence is the capacity of the mind to grasp, or comprehend, the good things of eternity and the means of attaining them. Through prudence we distinguish what is human from what is divine. The prudent Christian’s thoughts are on gaining eternity. Saint Thomas Aquinas said prudence is the eye of the soul. Without the light of the eye, we cannot find our way nor without prudence can we discern the path to heaven. Without the eye we cannot make full use of our limbs, nor can we practice virtue correctly. [It is something like spiritual common sense.] Its opposite is a worldly wisdom or wisdom of the flesh that brings temporal advantage or sensual enjoyment, but this is the wisdom of foolishness. (1 Corinthians 3:19).
Justice enables us to willingly walk the narrow path of the commandments; the just man dreads the slightest deviation from it. The just man gives everyone his due; to God, he gives worship, to proper authority, obedience, to subordinates, fairness, and to all, the love Christ commanded.
Through temperance a person uses the good things of life to the extent needed for attainment of heaven. He does not eat or drink more than needed to support life, preserve health, and fulfill responsibilities. The temperate person does not strive with excessive eagerness after honors, pleasures, or sensual enjoyments. [Editor’s note: this is not to say that pleasure, or fun, is wrong. It isn’t! Often, we need merely to indulge in moderation, an idea that is increasingly foreign to people today. The catechism says we are to avoid excess. See, CCC §2290. It has often been recommended to people who wish to grow spiritually to give up things that are not wrong so as to separate ourselves from worldly things that do not help us on our journey to heaven, and to do penance for past wrongs done to the others.]
Fortitude enables a person to make sacrifices willingly for the sake of the Kingdom of God. He who possesses the virtue of fortitude does not allow himself to be intimidated by ridicule, threats, or persecution. He is ready to suffer even death. He patiently endures all the afflictions that come upon him. He is like a diamond that no stone can break. Fortitude is more strikingly displayed in bearing great suffering than in undertaking great achievements, for suffering is more difficult than doing. “No saint was ever a coward. The holy martyrs showed fortitude in its highest degree.”
Rev. Francis Spirago, The Catechism Explained, Tan Books (1899) p. 444-46. Imprimatur, +Patrick J. Hayes, Archbishop of NY, Oct. 18, 1921.