“Mark 9:8, "where their worm does not die and the fire is not quenched," comes directly from Isa. 66:24, but whose voice are we listening to in the preceding verses? It might be Jesus, but then again, it might be anybody. Then as now, there were plenty of fire-and-brimstone preachers. And, since the climax of the pericope is a quotation of Isaiah, implying the whole thing is something of a sermonic commentary on it, we must deny it to Jesus. Again, who remembers the great man quoting someone else?”