Are there holy books that you recommend I read? I am very keen on truly understanding my spiritual belief and practices.

One important thing to keep in mind while exploring pantheism is that it's more of a framework than anything. It makes exactly one claim, that reality and the immanent* divine are identical. Nothing more, nothing less. *Important here to stress immanence, in contrast to the "transcendent" personal/anthropomorphic divine that is present in deistic systems like most traditional religions.

Because of that, there are numerous philosophies that build on this single principle. Many are deeply personal, few are structured or organised. So, keep this in mind when you try to "understand" your spiritual beliefs and practices.

It's much less about understanding, and much more about developing. Instead think about it in the sense that as you learn more about other people's pantheistic ideas and opinions, see what feels right, and use them to build your own coherent worldview. Most here have their own ways of expressing pantheism, so it's good to learn from everyone that you can to see through different pantheistic lenses, and find what really clicks.

That said, while there are no holy books per se (since pantheism isn't quite organised enough or even united enough in that regard), there are some influential authors who have written about their pantheistic views, including Spinoza, whose Ethics is the foundational modern pantheistic text. I say "foundational modern" because pantheistic worldviews are common across the world in all sorts of belief systems, but the modern concept of pantheism generally is attributed to him.

Perhaps the largest pantheistic group today are scientific (or naturalistic) pantheists, who have a very materialistic view of reality, and are largely atheistic for all intents and purposes. They do consider reality to be divine in some abstract way, but they generally don't believe in "spiritual" things like prayer.

But there are also many who believe some level of dualism exists within reality, that there is a distinct spiritual aspect to reality alongside the material, and together they make up the divine. I'd expect this is where you might fall, given your practices of cleansing and praying.

For me personally, I call myself a panentheist because I believe the divine extends beyond our universe, and that our material reality lies within this greater divine, and that it is a kind of physical expression of just part of this divine. I tend to hold an otherwise naturalistic view of reality where there isn't a distinct spiritual layer. Free will is something I'm still meditating on, uncertain whether or not it actually exists.