Jude
The epistle of Jude is a very short letter.The author exhorts his readers to fidelity, to cling to “the faith which was once for all delivered to the saints”. He says this because he is writing in response to the intrusion of false teachers into the Church. Jude condemns these teachers and makes this point again and again by drawing on example after example of those who were evil and suffered the the consequences of their sin.
This document holds an interesting place in the canon in that it warns its readers using Old Testament examples, examples from extra-biblical literature, as well as apostolic prophecy. In fact, the canonical status of this book was disputed in the Early Church over its use of apocryphal sources. However, this question was pretty much settled in the North African synods of the 4th/5th centuries.