Some initial disjointed thoughts
To me, this is the most baffling card yet. So, I'll focus on the more straightforward (or maybe that's even an assumption...lol) imagery here:
This whole card has a dark, strange, and mysterious (to me, at least) quality, which captures the High Priestess half of the feminine archetype nicely.
Lunar eclipse at the top? In the context of the Fool's journey, perhaps this connects Trump 1 to Trump 2--moving from a masculine principle embodied by the Magician to a feminine one. However, we're then left to explain the moon-like thing behind her legs.
When I look at this card as a whole, something strikes me about the figure of the High Priestess: She seems to be almost rigidly locked in place, unable to move (a depiction of passivity?). She appears anchored down into the water. Interestingly, we see here the tree motif again from the Magician. Like a tree absorbs water through osmosis, the HP receives wisdom through her strong connection to the unconscious.
Her feet are connected to or morph into--which is it?--branch-like structures that disappear into the water. Very strange. Must think more about the white flower and spirals/tendrils...
I also noticed the four breasts, which are connected to the ring, connected to the crescent moon (maybe?)... To me, this all communicates something about the connection between fertility and the moon.
Must. think. more. on. this. one. !!! Wow.