While mystical experiences are very personal, and are highly personalized, there are some broad categories experiences in which they are shared across people who have had them. They are oddly repeatable* even if they are not falsifiable. There are signatures that are in common, and you can recognize them. "Getting" Rumi for me was like this: After my own experiences, I stumbled back across Rumi and it suddenly made sense. I can see what informed his poetry, even across linguistic, religious, and historical lines.
This was the same with Tao Te Ching. What was impenetrably cryptic was suddenly intuitive. Or Zen Koans for that matter.
*They are oddly repeatable even across religious lines, even in cultures that may not have formal religions. It's not religion that makes the mystic.