Explain what you mean. When we ask the unchurched why they don't come to church, the number one complaint is they can't understand what's going on or what preachers are saying. We try to make no assumptions about what visitors will understand, and we work hard to talk the language of those unfamiliar with church.
Explain why. Postmoderns resist directive-type communication. A sermon that starts off with an authoritative statement about how people ought to behave turns them off. I've found it works better to speak persuasively, sometimes taking twice as long to explain a point. "If you believe this, so-and-so occurs; if you believe that, such-and-such happens."
From the book Growing Your Church Through Evangelism and Outreach.