Extreme Makeover featured a family that moved from suburbia to a rough Albuquerque neighborhood to make an impact. Early in the episode, Ty asked the father about his motivation. Faith was briefly discussed, but I felt this quote was a great summary of urban ministry as a whole:

I slept in the back of car behind a motel twenty years ago. And I fell in love with broken people. There is something inside of them that if you can dig in and find it they're amazing people that have deep, deep, deep experiences that nobody can touch. And when you get into a person's life and you see that come out of them, there is nothing like it.

I am one of the richest men I know because what I am doing fulfills me. And that is what it's really about. I want my life to count for something. I want for the city to look at this place and say it's not a throwaway. It's not junk. These are real people with real lives with real hearts and they matter.

I agree with most of it, especially the parts about the people whose lives he wants to touch.