If you are not familiar with Lesslie Newbigin's story, he grew up in Britain and studied at Cambridge, where he was converted and trained for the ministry. After getting married, he spent nearly forty years in India as a missionary. When he was in Britain as a child and a student, it was still something of a "Christian" society, but upon his return in 1974, he discovered a country that he could describe as nothing less than pagan.

Michael Goheen, in his doctoral dissertation on Newbigin's missionary ecclesiology (which is available online for free!), writes that Newbigin had come to understand the church's relationship to the culture as a missionary encounter because "the church embodies the gospel as an alternative way of life to the culture in which it is set and thereby challenges the culture's fundamental assumptions" (365). Newbigin borrowed language from the sociology of knowledge to express this notion of a missionary encounter in his book, The Gospel in a Pluralist Society. He writes,

The gospel gives rise to a new plausibility structure, a radically different vision of things from those that shape all human cultures apart from the gospel. The Church, therefore, as the bearer of the gospel, inhabits a plausibility structure which is at variance with, and which calls into question, those that govern all human cultures without exception (9).

Goheen adds that "all cultures exhibit a plausibility structure that embody and transmit the fundamental beliefs of its inhabitants. Those fundamental beliefs stand in opposition to the gospel and if there is to be a missionary encounter, the church itself must be a community that embodies an alternative set of foundational beliefs" (365-366). If the church is faithful in doing this then three things will result: first, the foundational beliefs of a culture will be challenged; second, the church will offer the gospel as a credible alternative way of life; and third, the church will call the culture to radical conversion and invite it to live and understand the world through the lens of the gospel. At that point, the culture is left with the choice of accepting or rejecting the gospel and the lordship of Jesus Christ. As Newbigin expresses it in his little book, The Other Side of 1984: Questions for the Churches, the church that embodies the gospel

must necessarily clash with contemporary culture. It must challenge the whole 'fiduciary framework' within which our culture operates. It must call unequivocally for radical conversion, a conversion of the mind so that things are seen differently, and a conversion of the will so that things are done differently. It must decline altogether the futile attempt to commend the biblical vision of how things are by seeking to adjust it to the assumptions of our culture (53).

The fact that Newbigin would say something this provocative in the context he did was significant, for he was speaking about a culture that, to some degree, still believed it was a Christian culture, much like America today. But Newbigin understands that just because a certain percentage of a culture's population professes belief in God or attends church regularly does not mean its underlying worldview is shaped by the gospel.

Further, he rightly recognizes that the worldviews that give shape to a culture are religious in nature. Religion, in Newbigin's view, is not just a cultural form, and "it is more than an institution that embodies beliefs and practices concerning God and the destiny of the soul. It is a set of ultimate commitments about the nature of the world that gives shape, direction, and meaning to life and demands final loyalty" (Goheen, 367).

And here, then, is the reason the gospel needs to challenge the foundational beliefs of a culture—because all of life is religion, and everything we think, say, and do is either in service to God or an idol. Christ is Lord over all of life, and the church is called to proclaim and embody this truth. As witnesses to Jesus and the presence of his kingdom and rule, we cannot be satisfied to accept a sacred/secular divide and leave our culture to let its presuppositions inform certain areas while challenging its assumptions in other areas. All of life belongs to the Lord and our calling as the church is to unapologetically call to the world to recognize that truth.