how, why, then
焉 is a classical function word that marks questions (how, why) or logical sequence (then). Its meaning is grammatical rather than concrete.
焉 is an ancient grammatical particle. Its visual origin is uncertain, though it may have originally depicted a bird or a similar object before being borrowed for its sound.
The top 正 suggests correctness, and the lower fire-like strokes suggest a question burning. Picture asking 'how' and 'why' until the answer is correct, then moving on.
For エン, imagine an English scholar asking 'how' and 'why' about an ancient text: English -> エン, and the questions lead to understanding.
end (of life); death; demise
ultimate fate of the universe; end of the universe
the eye is blind if the mind is absent
sudden; unexpected
no concern of mine; nothing to do with me
miswriting a word; using the wrong kanji to write a word