In many places, Edwards shows that Afghans generally had a strong attachment to Islam, and that it represented more than simply religious beliefs and practices as we might narrowly define them.
As an example, take the story that Wakil told about his father denouncing the minister of defense while they argued in the prison courtyard(pp. 109-10):
My father raised his head, and Mohammed Aref said, "Enough!" He was thinking that certainly he had been convinced and would take the land. But my father said to him, "You are infidels! You're not Muslims!" What he meant was that they didn't have compassion. "Tell your men that they have injured my arm! My arm is broken!"This respect for Islam however is not the same as the kind of Islamism familiar today in Afghanistan and other countries. Certainly religious leaders and holy men had a limited amount of clout back in the 60s and 70s. Edwards quotes Wakil as saying that government was not "the work of a mulla."
The mullas were fine for leading prayers or for giving a religious imprimatur to the results of tribal negotiations. However, their power was largely symbolic, and from the tribal perspective any group that sent such a representative to a national assembly would be admitting its weakness or declaring its disdain. (Edwards, page 118-9)
Elsewhere, Edwards shows an attachment to religious parties as one possible route for the deracinated to find a satisfying value system. More on this later, when I find the appropriate page numbers, but Edwards locates the new Islamist sentiment as coming from the University of Kabul, where it was in hot competition with Marxist ideology.
Update: Here is the text I was looking for, on p. 85.
[Actions of the Khalqi government] helped to define the ensuing conflict in Islamic terms. In retrospect, this seems almost inevitable, but at the time of the coup d'etat, Islam appeared to be moving in the direction of many Western religions: it was becoming a matter of personal belief rather than of social or political consequence. We know now what we didn't know then -- namely, political Islam, marching in competitive lockstep with Marxism, had been gaining a constituency in the schools and military, and radical Muslim parties had been making their own plans to take power for some time before the Marxist revolution. However, these efforts, like those of the Marxist parties, were confined to interstitial institutions such as schools and the military and were not widespread in society at large.Image: Young mullahs graduating, Kabul, 2008.