If you are interested in the Church and Early Christianity then this book is really a must have. There is an active table of contents here, but I should point out that for some reason the publishers have formatted this in grey, rather than black type.
First written some time in the First or Second Century A.D. (C.E), we only know a few things about this work. No one can say for sure who wrote it, although we do know that it was originally written in Greek, and then in Latin. This does appear in the Codex Sinaiticus and was very popular for a few centuries, with it being read aloud by even the clergy in church. An allegorical series of visions, mandates and parables this is of interest to laymen as well as scholars as it tells how to live rightly, in a Christian way.
This short book hasn't been without controversy over the years, and is non-Canonical and thus not in the Bible, but even so it is still worth giving it a read for those interested. With the advent of the Kindle and anyone being able to publish their own works there has been an increase in religious thought, texts and expressions, but probably nothing quite so elegant as this work.