READ: Psalm 19, Isaiah 16-18, John 12, Revelation 20
Three times in Revelation 20, the devil is referred to as a liar, a deceiver of nations (v.3). Being very good at what he does, the devil is canny enough to mix a fair amount of truth in his deception. The best lies are, after all, based on truth and have the ability to appeal to our emotions as well as our intellect.
Christian mission to Muslims hinges on how this non-Christian religion is evaluated. If your perspective is that Islam-while disagreeable-is redeemable, you approach the Koran and the ideology itself from a fulfillment model: you start with what the Muslim believes and lead him or her to a more biblical understanding over time. If your pre-suppositional starting point is that the devil skillfully wrapped a grand lie in small truths, then you advocate discontinuity: a break must be made with Islam and a new life in Christ embarked upon.
The genius of the devil is his ability to take wicked concepts and wrap them in partial truths. It is dangerous–if not foolish–to try and reach back into an integrated lie to rescue small truths if their reason for being was originally to obfuscate the deception. It is sheer madness to look into an antithetical text for proofs of your faith, for by doing so you undermine your own source of authority while giving credence to the opposing scripture.
Not all lies are equal, some lies are more insidious than others. There are lies in Judaism, yet the Old Testament is inspired. There are deceptions in Catholicism, yet the Catholic scripture includes the God-breathed New Testament. What distinguishes Islam from either of the above religious ideologies is that its authoritative text denies the deity of Christ–vehemently. It is impossible to reach into Islamic revelation to build a Christological case. You cannot take a text that lies about Jesus (forcefully claiming He is not God) to prove that He is God. Yes, there are small truths in the Koran, but if they were placed there with intent to deceive, we would be foolish to start with the Koran when trying to introduce a Muslim to Jesus.
In contrast to texts that deceive, Psalm 19:7-11 reminds us that the law of the Lord is perfect, sure, right, pure, clean, true, sweeter than honey, able to warn us, and a reward to those who keep it. John 1 reminds us that Jesus is the eternal Word of God, and John 14 assures us He is truth–there is no deceit in Him at all. All descriptions of who Jesus is (the most crucial clarification in history) must be based on a source that is completely true, big Truths wrapped in bigger Truths surrounded by only Truth. There must be no lie in our truth, there should be no lie in us.