Whenever we hear Jesus say in the Gospel that "You are the salt of the earth" and "You are the light of the world, the city set on the mountain," the danger for me at least is that I can get pretty full of myself, thinking "Yeah, I'm a pretty important guy, the world really needs me." Then I started thinking about this in the context of today's feast, that of the martyr St. Barnabas. As Christians, we really are that city on a hill, and when we live the Christian life, it is plain for everyone to see, both those who are attracted to it and those who are repelled by it. The danger of being like a city on a hill is that your enemies can easily find you and attack you. When we believe what the Church believes all the tough social issues today, abortion, homosexual marriage, contraception, and a host of other issues, we set ourselves up as targets because the world isn't even questioning the rightness of these things anymore, and that could lead us in the direction of St. Barnabas.
St. Barnabas was an early Christian, and a traveling companion of St. Paul. He owned land, but he sold it all and gave all the money to the young Church. He travelled far and wide, preaching Christ and truly becoming that city on a hill. But being a city on a hill eventually led to his enemies and the enemies of the Church finding him, and it led to his martyrdom.
Nonetheless, we are called to imitate St. Barnabas, and to be that city on a hill, to be the light in a dark world. It may lead to our martyrdom, no use mincing words there, but if we imitate his witness we will certainly imitate his joy in heave.