In the foreword, O. M. Burke describes three types of books about Sufism: books written by the Sufis themselves--past and present--which are intended to instruct; books by "outsiders" such as orientalists, who "are never aware of the method of extracting currently relevant materials from traditional ones"; and what he calls "museum materials"--superseded manifestations of Sufism on which imitators in both East and West have tried to build whole schools and orders.
According to Burke, The Dervishes of Turkey, a major source for many orientalists, combines the faults and virtues of the latter two.