Here's a clip from a great article that will point you to a new book (I have but haven't read yet) called unChristian.
This clip is profound especially to those who preach and are wrestling with what audience they ought to be speaking to: Christians or non-Christians. I'll be speaking to a group of college students this Friday night. I think this article is timely for me.
"One of the remarkable themes of the New Testament that seems too rare is the insider-outsider dynamic. This is hard for Americans – a very Christianized people with a rich Christian tradition – to fully comprehend. But Paul, living in a clearly non-Christian context, never seems to defend his rights as a Christian. Instead, Paul seems to accept a sinful and broken world, while holding the people of Christ to account. He is constantly writing in this dual role. He is an apostle (a leader of churches) and missionary (an apologist and evangelist to outsiders). He calls the Christian community to high standards and yet reaffirms that these standards do not apply to those outside Christianity (1 Corinthians 5 is one of the best examples of this). What is the point for preaching today? Since your preaching is heard by both Christians and non-Christians, you are both a leader of Christians as well as a missionary to unbelievers. Finding that right balance is incredibly difficult, but it can be done, with the help of the Holy Spirit. Part of this task, I believe, is to help your people see their role as missionaries to a culture that is now effectively post-Christian. You have to help train them to see the world in the same way Paul did."
I would add that if we are preaching through the word of God, the Holy Spirit will help you balance these two. I'm counting on that.
If you want a deeper understanding into this issue, David Kinnaman and Gabe Lyons’ book, unChristian: What a New Generation Really Thinks about Christianity…and Why It Matters, has much to offer.