Should the main idea of the sermon follow the main idea of the biblical passage in expository preaching? The question strikes at the heart of what we do. Text-driven preaching answers “yes” to the question. The text should drive the sermon otherwise we are in danger of using the text to support our ideas instead of submitting our ideas to the authority of the text. I agree.
However, some preachers do not agree. One preacher recently posted an article on www.preachingtoday.com entitled “The Main Point of a Passage Should not Always be the Main Point of Your Sermon.” He used 1 Corinthians 6:12-20 as his example. The main point of the passage, he wrote, was “don’t visit the prostitutes,” and that would not apply to the listeners in his congregation very well. He decided that he should not preach the main point of the passage as the main point of his sermon.

What is the big idea?

Every passage contains a big idea and many small ideas. The small ideas are the concrete, applications of the big idea. We must first discover the exegetical big idea before we can frame the homiletical big idea. When I look at 1 Corinthians 6:12-20 what strikes me is that “don’t visit the prostitutes” is not the big idea. The passage starts with “all things are lawful for me, but not all things are profitable (v.12) and ends with “therefore, glorify God in your body” (v.20). In between, Paul talks about food and sex. He argues that our bodies belong to the Lord so using them for sexual immorality violates our owner. The exegetical big idea should center on using our bodies to glorify our owner. Paul applies that big idea to food and sex both of which were associated with the pagan worship of idols.
Once we correctly identify an exegetical big idea, then we can begin to frame our homiletical big idea. The exegetical big idea informs the homiletical big idea, but it is not identical to the homiletical idea. The preacher must transform the exegetical idea into the homiletical idea to get the big idea. The big idea is shaped not only by the meaning of the passage but by the purpose of the sermon, and the purpose of the sermon is directed by the needs of the people in the congregation.
How do we transform the exegetical idea into the homiletical idea? 

Step #1: Make it personal.

Bruce Shelley writes, “The big idea of an expository sermon should be developed as a personal truth” (Willhite and Gibson, The Big Idea of Biblical Preaching: Connecting the Bible to People, p.97). I start shaping my big idea by asking how the exegetical idea applies to me. I am not tempted to frequent prostitutes, but the big idea still applies to me. My body is the Lord’s, not mine. He owns it. I must use my body for His glory. God calls me to sexual purity because what I do with my body implicates my Lord.

Step #2: Make it theological.

Sometimes our preaching can become atomistic by reducing the message to the unconnected elements in a passage. We end up preaching the building blocks without showing people the building, the molecules instead of the body. Consequently, the sermon on 1 Corinthians 6:12-20 preaches against eating food offered to idols and sex with prostitutes, the elements of the text. But the big idea requires us to think theologically. We turn small ideas into big ideas by connecting them to the theological themes of biblical theology. In this passage, we see themes of redemption, Lordship of Christ, the temple of the Holy Spirit and the glory of God. These themes should shape the big idea.

Step #3: Make it relevant.

Our people come to church on Sunday having wrestled all week with a sensual, hedonistic culture. Sex sells everything from cars to clothes. Our listeners don’t go to a temple to engage in socially acceptable but sexually impure activities. The temples of our world are shopping malls and search engines. The better I listen to my people, the better I can transform the exegetical idea into a big idea that preaches. The big idea of the sermon must be framed by the needs of the people as they intersect with the passage. The big idea of the sermon is shaped by the audience and can be framed differently for different audiences.

Step #4: Make it visual.

The world today is highly effective at visual story-telling. We are awash in visual images. Movies and television are filled with sexual imagery subtly persuading us to think wrongly about our bodies. Terry Mattingly points out that advertising preaches a visual sermon, see the image, buy the product and accept the result by faith. “Millions of people,” he writes, “make professions of faith at the shopping mall” (The Big Idea of Biblical Preaching, p.87). Our sermons need to turn ears into eyes. People need to see the big idea that connects the Bible to their world. 
What’s the big idea? The big idea is a personal, theological, relevant and visual statement that shows people how the Bible speaks to their situation.