Sin. What is it and why would a homeless shelter insist on talking about it?
Sin is the divergence from the rules and order designed by God. Acknowledging the existence of sin implies a particular worldview—one in which God created the world and has authority over it. He has the right—the responsibility, even—to make the rules, and the rules He makes aren't arbitrary. They are meant to lead us into the fullest, richest lives possible.