Jude Alludes to Enoch

The quotation in verse 14 is the obvious one. The allusions are everywhere else, and they are harder to see only because we were not raised on the source.
The chains and gloomy darkness in verse 6 are the language of 1 Enoch 10 and 21. The order Jude marches through his examples in - rebel angels, then the flood generation, then Sodom - is the Enochic sequence, and it is the same order Peter uses in 2 Peter 2. These are not scattered borrowings. Jude is working inside a framework his readers already had.
Scripture links:
- Jude 6-7 - The sequence: angels, then Sodom, in Enochic order.
- 2 Peter 2:4-6 - The same sequence, independently.
A letter this short does not repeat a structure by accident.