How can a force that transforms convicted murderers into placid samaritans, and that has given the world Handel's ''Messiah,'' the mosaics of Ravenna and Borobudur Temple also have spawned the Salem witch hunts, Osama bin Laden and columnists who snarl that America should invade Muslim countries, ''kill their leaders and convert them to Christianity''? What sort of Jekyll-and-Hydra-headed beast is this thing called religious faith?