It contains technicalities (to send dead souls were they believe they belong, and directions how to do that, which do not make sense unless you're familiar with transdimensional travel), code of conduct, and a big collection of famous psychopomps to copy or use as inspiration for one's own image.
The first part is sparsely illustrated with transdimensional maps (familiarity with which the reader is assumed to have, or obtain elsewhere; there are no detailed explanations), the last richly with works of art by the people who believed in the pictured "Death".
As all mercurial books, it appears to any reader to be written in the language they are most comfortable with reading.