Jude’s fruitless autumn trees, twice dead
Here’s what it means
False teachers are barren, lifeless, and destined for uprooting and judgment.
Why the Bible says it this way
The writer deliberately uses very strong language to make an important point. The point is serious even though the wording is not meant literally.
A helpful detail: “Twice dead” intensifies complete fruitlessness and doom; it is not a biological category.