The Bible calls us to be salt and light. Those things only have impact with proximity (closeness). The salt effects what it touches and the light effects where it goes. If we hide the light in our basement, it won't do much to light up our world. If we only bring it where things are already light, it won't do much brightening. We need to involve our lives in other people's lives if we really want to make a positive difference.
A friend recently showed me this video, it's great. It can also be viewed at, http://www.youtube.com/watch?v=uhOJW4Uwy3c