Courage is the virtue that allows you to practice all the other virtues, even when it's frightening or uncomfortable to do so.
To practice honesty, for example, you must be willing to say things that are sometimes difficult to say. To practice generosity, you must be willing to give of yourself and your resources, even though there's a change that giving might cause you to suffer. To practice forgivenes, you have to let go of the victim mentality and acknowlede that you choose how to respond to any aggravation or wrongdoing.
Courage is the bedrock virtue because it allows you to step into that uncomfortable place and practice all other virtues.
The student need [subjunctive mood form] only turn to literature for examples of how courage fortifies one's life, and how without it, a person is spiritually weakened. In Nathaniel Hawthorne's The Scarlet Letter, for example, the Reverend Dimmesdale hides his sin of passion because he lacks the courage to confess before his Puritan community and be in disgrace as a minister. But because of his spiritual timidity, he lives in fear of his Puritan God and others. Moreover, all good works that he performs are false because he is a hypocrite, pretending to spiritually advise people when he hides sin himself. No matter what he does, Dimmesdale is dishonest. In Chapter XX, Hawthorne as narrator comments,
No man, for any considerable period, can wear one face to himself and another to the multitude, without finally getting bewildered as to which may be the true.
Eventually, of course, his secret sin causes the minister such agony that his health deteriorates until in desperation and overwhelming guilt, he makes a public confession.
Another character of the same novel is Hester Prynne, having borne Dimmesdale's baby, is forced to admit her sin; consequently, she is scorned by the Puritan community and made to wear a scarlet letter constantly on all her clothing. However, with courage, Hester repents for her sin and performs acts of the virtue of charity such as tending the ill and dying. Her good deeds do not go unnoticed and the community begins to perceive her as a woman of courage and worth.