Gerhard Hasel. This masterpiece on the subject by the late Dr. Hasel is indispensable for any library. This book investigates the nature of speaking in tongues by Christians and non-Christians. It addresses tough questions such as: whether tongue-speaking is from God, the demonic, or other sources, whether tongue-speaking will unite all Christian churches and religions, and whether all Christians need to speak in tongues. PB 176 pg.