The book of Jude is a tiny book, tragically neglected by students, yet overflowing with fascinating Old Testament references and allusions: lessons from Israel in the wilderness, the angels that sinned, the strange events of Sodom and Gomorrah, and other insights from Cain, Balaam, as well as the mysterious person known as Enoch.
Jude is written for the end times, for the end of the Church Age.
Jude is the only book devoted ENTIRELY to the great apostasy. Jude is the "vestibule" to the book of Revelation..