In Above All Earthly Pow’rs: Christ in a Postmodern World (retold in The Supremacy of Christ in a Postmodern World, free book here and audio: 2006 Desiring God National Conference ), David F. Wells has a fascinating story that demonstrates the necessity of contextualization:
The country’s ambassador was an American who has lost his seat in Congress and wanted a judgeship. That didn’t work out, so he settled for being an ambassador to Sarkhan. He did not believe in trying to understand the history and the customs of the people of Sarkhan, and he discouraged the embassy staff from doing that too. And in this account, the United States sends off to Sarkhan a gift of rice, and so it’s carried to Sarkhan in American ships, transported in American trucks. It is a wonderful ceremony. There are all these American officials standing around, making a formal presentation of this gift. What they don’t realize is that some Communists sneaked in and stenciled “This Is a Gift from Russia” on the bags of rice, written in Sarkhanese. So here you have the American officials making these very formal speeches about this gift that they’re giving, and the problem was they didn’t understand the language. They didn’t know what was actually happening and what the people understood from the ceremony.
…Theology is undoubtedly about timeless truth that we have in Scripture under the inspiration of the Holy Spirit. But it is timeless truth that needs to be brought by God’s people into their own particular context.
This, right now, has become a very agitated discussion right across the front, and it’s especially interesting in missionary circles. There is a movement now among some missiologists who are arguing not simply that missionaries should adapt the culture of the place where they go—dressing like them, learning their customs, language, history (what the ambassador should have done in Sarkhan)—but they’ve actually gone one step further and argued that people can receive Christ within the context of other religious cultures such as Hinduism and Islam. They can receive Christ without leaving those contexts and religions. So in this missionary context you really don’t have a church, because, of course, a church would very often imperil Christians: the moment they’re baptized, they get killed. This is a way, they’re arguing, to penetrate these cultures.
Here, in my judgment, a line has been crossed that is fatal to the gospel and to Christian faith, and derogatory to Christ. What you really have is a synthesis, the paganism of the Old Testament against which the prophets prophesied. We can’t have Christ and these other religions, but we also can’t have Christ and our own cultural practices where those practices and those beliefs violate what an understanding of Christ and a following of Christ requires. So it requires discernment on our part to see how we can get alongside people and speak their language, learning what habits, practices, and customs we can adopt without violating the truth, but also how that timeless truth can be made to intersect with the way in which people think.
Finally, he contends that expository preaching must be contextualized:
I happen to believe principally in expository preaching. But if I have a critique of expository preachers, it is that some of them think that once they have unpacked the truth of a text, they’ve done their work. And sometimes this is reinforced by the belief that the Holy Spirit will accomplish what they haven’t done. God in his grace undoubtedly does do that, but if simply reading the Bible was sufficient, why would God have given to the church teachers and preachers or teaching preachers? Preachers need to take that additional step. And especially here in America—as people are coming out of an increasingly paganized culture where the Christian memory gets more and more distant, where people in the pews understand less and less or bring less and less of a Christian worldview with them—it becomes more and more imperative for preachers to make sure that the truth they are preaching intersects with what is going on inside people’s minds. The line must be drawn so clearly that people in their own lives know whether they are being obedient or not, and what they should do with that truth when they have heard it. Now that is contextualization. It goes all the way from people sitting in pews in America to missionaries who are doing their evangelism in a Hindu or Islamic context. (pp. 168-170)
God in the Wasteland: The Reality of Truth in a World of Fading Dreams is the one best book I’ve ever read.