A mystery surrounds a guest at the Golden Generation Retreat Center, 30 miles northeast of Allentown — Fethullah Gulen, one of the world's leading Islamic thinkers. Concerns in the U.S. about Gulen and the spread of Islam are rooted in ignorance and misunderstanding, said Terry Rey, chair of the Department of Religion at Temple. "Any religious movement that begins to draw people is a threat to someone," Rey said. "As a scholar of religion, I can contextualize it, and I cannot see it as anything fundamentally different from what has always gone on."