What Is the Insider Movement
At the risk of being too succinct, IM is the missionary perspective that new believers from Muslim backgrounds ought to be left in their Muslim context. In other words, let the Muslim stay Muslim as long as he is now a follower of Jesus.
Why Is there an Insider Movement?
There are many reasons why IM became so popular:
1 - It's a lot easier for someone raised Muslim to say "I'm a Muslim who follows Jesus" than to say "I am no longer Muslim; I'm Christian"
2 - It's much easier for families to accept new followers of Jesus if they are still regarded as Muslim
3 - Missionaries feel better about their efforts, because they see an exponential increase of "fruit" when before they had little
4 - It's easier to raise funding at home when reporting massive success abroad
5 - It creates less conflict, more warm fuzzies.
6 - (This deserves it's own number) Some missionaries use this approach to preach to Muslims without having to explain or defend that Jesus is God.
What's the Problem?
The problem with IM is that traditional Islam is not compatible with following Jesus. Islam denies the very purpose for which Jesus was sent into this world (his death on the cross for our sins; cf. Qur'an 4:157) and it denies the divine nature of Jesus (Qur'an 5:72, 5:116).
To risk perhaps going too deep into my opinion: many Westerners distinguish between culture and faith from a Western perspective, understandably but regrettably so. For example, people in the West often call themselves "Christian" or "Jewish" while separating themselves from the beliefs of their faith, to the extent of even having disdain for it. This distinction cannot be applied to Islamic culture the way it can in the West; although Muslims do not always believe what the religion traditionally taught, almost always you will find their allegiance lies with Islam, and they will rarely separate themselves from it. So when a Muslim follows Jesus, he is first a Muslim, and then a follower of Jesus. That just doesn't work.
Where Do We Draw the Line
I must be clear: I think we ought to contextualize the message, as much as possible. If a BMB, believer from a Muslim background, wants to say "Allah" instead of "God", by all means feel free. (FYI: Arab Christians used the term "Allah" even before the advent of Muhammad and Islam. They still do.) If a BMB wants to pray on a prayer rug, pray away!
Where I draw the line is when we compromise the Gospel. Which is why we must be absolutely clear what the Gospel message is: God incarnate, Jesus, died on the cross for our sins and rose from the dead on the third day as the firstborn of the resurrection that God may be glorified through our eternal salvation.
If an Insider decides to contextualize everything except the Gospel, I'm fine with that! But the moment Jesus' deity is compromised, or his death on the cross for our sins, or his resurrection from the dead, then we are preaching a false gospel. And God has already judged such people:
"But even if we, or an angel from heaven, (or someone in the Insider Movement) should preach to you a gospel contrary to what we have preached to you, he is to be accursed!" Galatians 1:8 NASB, the parenthetical is mineSummary
The Insider Movement has the right heart, and I embrace the concept as long as it does not go too far. Unfortunately it often does, and we need to be on guard against a false Gospel.
See Alan Shlemon's recent article on STR:
Muslim Followers of Christ? A Look at the Insider Movement
See Lingel et. al, Chrislam (even includes contribution from IM proponents)
Chrislam on Amazon