In his treatise On War Against the Turk (1528), Luther develops more fully his assessment of Islam in the context of justifying a violent response to the Turks. He offers three observations about Islam based on his reading of the Qur'an. First, he argues that Muslims believe that Muhammad is superior to Christ and that Christ, while without sin, is merely a prophet and not humanity's savior. Muhammad undermines the very heart of the Christian faith, leaving his readers with a "doctrine of works" that places Muslims in the same category as Jews and Catholics in rejecting justification by faith. Such a doctrine is the work of the devil.

DEFINE: Explains justification by faith as the doctrinal lens through which Luther classified Islam with Judaism and Catholicism.

Green, Todd H, The Fear of Islam_ An Intro…, loc. 150