the tongue is only the fuse; the source of the deadly fire is hell itself (lit., “Gehenna,” a place in the Valley of Hinnom south of Jerusalem where human sacrifice had been offered [Jer. 7:31] and where continuous burning of rubbish made it a fit illustration of the lake of fire).
Blue, J. Ronald. “James.” The Bible Knowledge Commentary: An Exposition of the Scriptures. Ed. J. F. Walvoord and R. B. Zuck. Vol. 2. Wheaton, IL: Victor Books, 1985. 828. Print.