Commenter cl asks why I didn’t provide the full William Lane Craig quote about “instruments of Satan” in this post. The answer is that I was trying to be concise, but here’s the full quote anyways, with key parts bolded:
My experience as a young Christian of seeing some of my college classmates lose their faith left a deep impression on me, and when I began teaching I resolved to do all I could to help my students stay in the faith while still exploring the intellectual issues about the faith. In particular, I resolved never to present objections to Christianity without also presenting and defending various solutions to those objections. One of my colleagues who did not follow this method was causing some concern among certain Christian students in his classes. “I was only trying to get them to think,” he explained to me. “I was just playing the devil’s advocate.”
Those words hit me like a dash of cold water. For him they were merely a manner of speaking, but it was their literal sense that struck me. Playing the devil’s advocate. Think of it: to be Satan’s advocate in the classroom! That is something we must never allow ourselves to become. As Christian teachers, students, and laymen, we must never lose sight of the wider spiritual battle in which we are all involved and so must be extremely wary of what we say or write, lest we become the instruments of Satan in destroying someone else’s faith. We can challenge people to think more deeply and rigorously about their Christian faith without encouraging them to doubt their faith.
This is from p. 34 of Craig’s book, Hard Questions, Real Answers. Crossway Books, 2003.