Some of the words have been reversed but it doesn't mean that they're grammatically or syntactically wrong

Some of the words have been reversed but it doesn't mean that they're grammatically or syntactically wrong. The author just used that kind of word arrangement to make it more poetic and dramatic at the same time.

Syntax - arrangement of words to create meaningful sentences, clauses, and phrases.

In the poem, Jabberwocky by Lewis Carroll, some of the words, specifically the subject and the verb have changed position to create an emotional effect. It doesn't mean that if the verb comes after the subject, it is merely wrong.

Passage from the poem:

1)All mimsy were the borogoves

All mimsy - adjective / descriptive word Were - verb Borogroves - subject

*The adjective comes first for the author wants to emphasize the description of borogroves so the readers could picture their appearance.

2)So rested he by the Tumtum tree

Rested - verb He - doer / subject

*I used this kind of style if I want to emphasize the action. But it doesn't mean that the sentence is incorrect or its structure.

So in my analysis, syntax is used here for better emphasis of the things the writer wants to be conveyed by the readers. But we must consider that if you want to reverse the position of your words, do not separate the adjective nor the verb far from the subject. It should always come together.