But in Islam, as in Christianity, it is necessary to distinguish how the faithful behave from the way their faith teaches them to behave.
Context is important, and here Lippman is trying to distinguish between what a few radicals do outside of the larger belief system. Aside from that specific instance of decoupling mujaheeden from the American’s image of Islam, I don’t think that statement is quite correct.
Given that a religion provides a model for behavior and moral and social order, the results should inform an observer a great deal about that religion. If a religion teaches peace, humility, and assistance while its adherents wage war, put themselves above nonbelievers, and turn away from those in need… then either those teachings are not central to the religion or it is an extremely ineffectual religion. In this case it makes little sense to even connect people and events to that religion.
Then again one man’s explanation for lightning is another man’s means for organizing millions.