Working through the Sermon on the Mount on Sunday mornings, a few weeks ago I preached from Matthew 5.13-16, the Salt & Light passage. What I explained to our congregation is that, after instrucitng us about what our attitude ought to be as citizens of the Kingdom, Jesus goes on to reveal the Influence he expects his people to have on the communites where we live, and on the world around us.
In this video Tim Keller offers his thoughts about being Salt & Light.
GRACE & PEACE 
I Think you have to do & be both..transform culture by living out our faith in everyday life and at the same time tell people about the Redeemer. Being salt and light, to me means both. They must go hand in hand.
I think about the term “friendship evanglism”…there comes a point where the Gospel has / needs to be presented.
Action alwasy speaks louder than words.