I find articles and discussions about authorial intent interesting because, as an author, I don’t always intend some of the things that turn up in my books. Sometimes I will be writing a book, or reading a draft in preparation for editing, and be hit by something in the text. It won’t be something I deliberately put in there, but it will be something that’s there anyway.
For example, it took me way too long to realise that Mira was named after Amiron. I named both of them and I’d used a naming pattern for other characters where male names end in “on” and female names end in “a”. When I realised the connection, it clarified some of Mira’s motivation, some of the emotion behind her actions, but I noticed it after I’d already written the foundations.
I’ve just finished the first draft of a book that includes a scene discussing fancy dress costumes two of the characters had planned to wear. I included that scene because it gave nice insights into those two characters, their relationship, and their relationship with another key character. It was only after I’d written the scene that I realised there were parallels between the story I had planned for them and the two characters they planned to dress up as. Holy freaking foreshadowing, Batman! It wasn’t a conscious decision. Either I got lucky, or my subconscious is cleverer than I knew.
When I see something like this in an early draft, I can choose to work with it and build on it in the later drafts, in which case it becomes intended. That said, whenever I recognise something like this in my drafts, it makes me wonder if there are other things in there that I didn’t notice.
A lot of foreshadowing and symbolism in books is put there deliberately by the author, but it’s always worth remembering that these things can be in the book without the author intending them. It doesn’t make them any less real. If you spot symbolism/foreshadowing/parallels, then those things are there, even if the author didn’t realise they were writing them.
And if you’re a writer, don’t worry too much about trying to put the clever symbolism in right from the start. It may be that you get to the end of the first draft and see things you can build on later.