I am assuming that your basic question is how to make money by reusing quotations from books, particularly spiritual.

This idea is out there but if your quotations are amenable to memes then you could create a collection of them and offer them as a subscription or sell them on stock photography sites.

There are a number of meditation type apps that are filled with quotations. You could approach them to see if they would like to license your content. It doesn't seem like a huge market but as a developer of one of these apps I can see having this thought "I need to get inspirational quotes to go here and I don't want to build my own database of them...can I subscribe to an API that will give me these?"

It seems to me your quotations could help lead people to buy your books. If you were looking at all quotations in your business then how about an app that helps generate quotations from a book and turn them into ready made ads?

If I were looking for spiritual books and I can see myself browsing a collection of quotations from a book before deciding to buy, as this would help me sample the feeling the book may give me.

Put this all together I can see an inspirational quote service but I don't know if it would drive sales. I think you would do better to find a way to "disintermediate" amazon on spiritual books. A quotation becomes a sort of meme that you share on social media that drives people to this site. So they are to some extent prequalifying themselves since the quotation resonated with them. If they then see a number of quotations that resonate further they may choose to purchase a book.

So that's a lot of spitballing. I hope something in here helps trigger an idea for you to move this forward so you can realize the most from your writings.