The particular background into which an NT letter was addressed can sometimes emerge into clearer focus from a study of the unusual details and so enable a sharper application of the text.
This is the case with the short epistle of Jude. Looking at this letter through modern eyes we are struck by a number of rare features. Perhaps the most obvious is the close similarity between Jude and 2 Peter. At first glance the parallel seems so close that we might wonder why Jude's letter was necessary at all. It seems almost to be a duplicate of a large section of Peter's material. Then there is Jude's near obsession with angels. Celestial spirits are of course, referred to elsewhere in the NT. But in this short letter of just 25 verses, there are at least four separate references to angelic beings, vv. 6,8,9,14. Why this preoccupation?.
A further peculiarity, which particularly jars in the minds of evangelical Christians, is the fact that twice Jude quotes from extra-Biblical books. In v9, he alludes to what scholars say is the lost ending to an inter-testamental book called The Assumption of Moses. Later in v14,15 he cites the beginning of a similar work, this time The Book of Enoch. These books were probably written some time during the second or first century before Christ. Though Jude quotes from them, the church has always excluded them from the canon of Scripture. The question arises, 'Why has Jude chosen to use these works ?'