One of the things I love about the phrase is how it is a dichotomy. Courage and kindness are not synonyms--rather they have almost opposite connotations. Courage is powerful, while kindness is soft and compassionate. Courage takes charge, while kindness simply serves. Courage strengthens the weak, while kindness comforts the broken.
Yet, one without the other is incomplete. Courage without kindness is a dictatorship. It becomes harsh and uncaring. Kindness without courage is powerless. Without the strength to stand, it waffles and bends and is trampled over. Only together do they become truly virtuous. Courage strengthens kindness, giving it the strength to make a difference in this world. Kindness tempers courage, allowing one to lead with patience and mercy.