Christianity Today

C-2 refers to a "traditional church using insider language." This church is the same as a C-1 community but worships in the language of the Muslim population (such as Arabic or Turkish).

C-3 refers to "contextualized Christ-centered communities using insider language and religiously neutral cultural forms." These churches adopt the language of the surrounding Islamic community and embrace nonreligious cultural forms, such as folk music, dress, and artwork. A C-3 church would filter out any religious forms specifically associated with Islam. The majority of members are MBBS.

C-4 refers to "contextualized Christ-centered communities using insider language and biblically permissible cultural and Islamic forms." These churches adapt Islamic forms as long as Scripture does not explicitly forbid them. C-4 communities accept Islamic terms for God (Allah), Islamic prayer (salat), and the Gospels (Injil). Most C-4 churches follow the Islamic practices of avoiding pork and abstaining from alcohol. C-4 believers normally call themselves "followers of Isa al Masih" (Jesus the Messiah) or members of the Isaya Umma ("Community of Jesus"). The Islamic community would not view C-4 followers as Muslims.

C-5 refers to "Christ-centered communities of 'Messianic Muslims' who have accepted Jesus as Lord and Savior." These followers of Isa remain legally and socially within Islam. The Muslim community views them as Muslims. They reject or, if possible, reinterpret features of Islamic theology that are clearly incompatible with biblical faith.

C-6 refers to "small Christ-centered communities of secret/underground believers." These are believers living under the threat of persecution and retaliation from the government or their family or community if others knew they followed Jesus. They worship Christ secretly. If discovered, C-6 believers would almost certainly face prison or death.

Most mission workers today accept C-4 as the most appropriate form of contextualization. The current debate has largely centered on C-5 believers. They are not actually Muslim-background believers, but Muslim believers. They retain their Muslim identity. They regard Muhammad as a prophet—not in the "final" sense that Muslims claim, of course, but as a man who led the peoples of Arabia out of polytheism and into monotheism.

The current debate about C-5 believers centers on five key issues. First is biblical precedence. Scholars seriously debate if the Acts 15 Jerusalem Council decision regarding Gentiles applies to insider movements and, if so, how does it apply to both the cultural and religious identity of Gentiles.

Second, scholars debate the relationship of personal salvation to identifying with the larger church and other Christians. And they wonder how much a true Christian movement needs to confess historical Christian doctrines in order to truly be Christian.

Third, there are many who ask if it is ethical to encourage followers of Jesus to retain their Muslim self-identity—the key difference between C-4 and C-5.

Fourth, scholars debate whether C-5 groups are a new phenomenon, or whether they are merely an extension of issues rooted in the Protestant Reformation.

Finally, scholars debate whether C-5 represents a valid, permanent movement in the Islamic or Hindu world, or whether they are an acceptable transitional bridge that will eventually lead Muslims and Hindus into explicit Christian identity.

Amid the debates, one thing is clear: Christ-loving movements are growing in countries where a traditional church has been absent or long gone. Both theologians and on-the-ground leaders will need to reflect with care on the C-1 to C-6 debate as the gospel takes root in new contexts.

Timothy C. Tennent is president of Asbury Theological Seminary, where he teaches world Christianity, and coauthor of Encountering Theology of Mission: Biblical Foundations, Historical Developments, and Contemporary Issues (Baker Academic).