Courage is the virtue that enables a person to restrain fear in the face of danger, difficulty or doubt. As Nelson Mandela put it, - Courage is not the absence of fear, but the triumph over it.
Courage guarantees other qualities:
Courage enables people to face tough consequences for their acts. For instance whistleblowers like Edward Snowden often pay a heavy price for disclosures.
Without courage it is difficult to display qualities like leadership which entails laying out roadmaps for the future amidst uncertainty. For example it is courage that enabled Mahatma Gandhi to display the virtue of nonviolence against the oppressive colonial regime.
It encourages people to take firm decisions and attempt things that they have not tried before. For instance, it takes courage to invest in novel & seemingly impractical/commercially unviable ideas like the SpaceX.
Various personal, social and professional feats are unthinkable without courage. It may be the fight for social reforms or fearless decision-making by public officials to bring about public accountability, impartiality and truthfulness in daily life.
However, it must be borne in mind that courage must stay within limits defined by reason (like the courage displayed by law-enforcing personnel vis-à-vis criminals). Moreover, life provides daily opportunities and instances of courageous acts (for instance standing up for injustice, actively supporting a just cause like cleanliness in public places etc.) as distant from notions of courage as extreme or dramatic physical heroism.