Answer
The insider movement is an attempt to follow Jesus and rely on Him for salvation within the language and customs of one’s native culture. Romans 1:16-17 is given as validation that salvation is a matter of faith, not of a particular culture. The idea actually began with Paul, who fought against the assumption that Gentile Christians would have to meet Judaic requirements, and was validated by the early church when they decided Greek believers did not have to be circumcised (Acts 21:17-25). Later, the philosophy was realized when the Bible was interpreted into languages other than Greek and Latin. Modern missionaries to countries that are not Christian-friendly often rely on the insider movement. They feel it allows people to come to saving faith in Christ while maintaining their ability to witness to friends and family as well as safeguarding their lives. In this modern form, as in the old, it comes down to three issues: culture, religion, and theology.
The Insider Movement - Culture
There are very few Western Christians who would insist that a person from another culture sing only English-language hymns. Or only pray sitting in a chair, hands in lap. Or hold a church service with songs, announcements, and a 45-minute sermon every Sunday morning with coffee and cookies beforehand. But Jesus-followers in non-Western parts of the world maintain some cultural practices that are not so acceptable to Westerners. In many countries, parents arrange the marriages of their children. In others, it is disrespectful for a woman to not cover her hair or for a man to not have a beard. In some areas, it is inappropriate for a local believer to refer to himself as "Christian." Christian does not mean someone who follows Jesus and tries to live according to His teaching. In Eastern countries, Christian means someone from Europe or North America who lives a greedy, immoral lifestyle as seen on TV. To many, Christianity is not a religion or a faith system. It is a label for the Western culture.
Should culture be an issue? Can a person follow Christ within his or her own culture? As much as Westerners can follow Christ within theirs. There are parts of every culture that do not align with the Bible. If a certain practice within a culture does not agree with the Bible, that practice should be abandoned by believers within that culture. But if the Bible doesn’t mention a certain practice one way or the other, it shouldn’t be an issue. And, scripturally, there is nothing wrong with a group of believers coming up with their own word for "little Christ." No one is required to use a Greek word from 2,000 years ago. God looks at the heart, not the label.
The Insider Movement - Religion
The expression of religion is the point where Western Christians have the greatest problem with the insider movement. First, a little background. The "insider movement" concept is most common among missionaries to Muslim nations. The integration of a church into a culture can be designated by the labels C1 to C6. At one extreme is C1, which refers to a completely non-integrated, Westernized church with traditional hymns and English speakers in the midst of a native culture. At the other is C6, which refers to a small group of believers who keep their faith secret for fear of persecution. C1 through C5 are differentiated by increasing acceptance of cultural norms, such as language, dress, and worship style, with the gradual addition of religious practices, such as dietary laws and the use of native religious terms, such as Allah. C5 is the most controversial level, as worshipers still identify themselves culturally and even religiously by their national religion, although they claim their salvation is through Jesus. Advantages include the potential to witness to friends and family in a non-threatening way and a limited change in lifestyle.
Can a person be a Christ-follower and still call himself Muslim? Is it appropriate for Christ-followers to observe Ramadan, pray in the mosque, and study the Qu'ran? At what point does the culture of Islam cross over to the spirituality of Islam? It’s a slippery slope, and one that "Muslim-Christians" might respond to with another question: why do Western churches so often embrace the crass commercialism and love of entertainment found in Western culture? Whereas proponents of the insider movement equate a C5 believer with a Jewish convert in the early church, this is not an even analogy. The Jewish convert was transitioning from a legitimate, God-given religion to a more complete fulfillment of that religion. There was nothing unbiblical about Judaism! Conversely, C5 believers also compare their situation with the early Gentile converts who were not required to leave their culture to follow the “new religion” of Christianity. This is inaccurate as well. Nowhere does the New Testament say that new Gentile converts continued to sacrifice to Greek gods. In fact, it was their very rejection of emperor worship that led to the martyrdom of so many.
The Insider Movement - Theology
Seldom do insider movement arguments bring up theology. And since there is no standard for the movement, perhaps there is no standard to argue. Aside from the wrong theology of accepting Muhammad as a prophet and the Qu'ran as inspired scripture, there’s the matter of the person of Jesus. The Qu'ran speaks highly of Jesus. He is identified as a holy prophet and a teacher worth listening to. But, according to the Qu'ran and Islam, Jesus is not the Son of God. He is not God; He is not divine. Muslim-sensitive Bibles replace "Son of God" with "Word of God" or even the "spiritual Son of God" so as to be more palatable. When the sacrifice of Jesus is mentioned in C5 evangelism, it is as a traditional sin offering, not as God come to earth to save mankind.
The wording is understandable, if unfortunate. Muslims are monotheists with no acceptance of the Trinity. Jesus as God is heresy to the Muslim faith. Allah alone is to be worshiped and adored. Worshiping Jesus as "Lord" is heresy. A religious environment that does not teach that Jesus is God cannot be conducive to spiritual growth. Missionaries who approve of the insider movement claim that the realization of the deity of Christ comes later, after careful study of the Bible, sometimes years after the person has decided to follow Jesus’ teachings.
Is the insider movement an appropriate evangelical tool? To a point. It is certainly acceptable to worship God within one’s cultural framework—as Christian rock bands and praise-hula teams can attest. Jesus-followers of all cultures should be able to express their devotion in ways that have personal significance. Theologically, however, the insider movement is precarious. We are not to be of this world (John 17:16), even if it means the world hates us (John 15:18-19). It does take time to really understand Jesus, who He is and what He means, and it’s natural for new converts to feel they have their feet in both worlds for a time. But continuing one’s native religious practices and following its spiritual teachings—whether in Islam, Hinduism, Buddhism, or other—is not what the life of a Christ-follower should look like. Not every Christ-follower has to take the name "Christian" and sing ”Amazing Grace,” but he does need to worship Jesus, the Son of God, as his Lord and Savior.