You find books about Shar and Selune throughout the game, but they are easy to miss, I guess. I never thought, how it would be for new players, but since you mentioned it and Shar is heavily featured in the game, they maybe should invest in a scene explaining her a bit more for new players.
It's not like Abdirak and his goddess Loviatar - I'm pretty sure you can go through the game without indepth knowledge of Loviatar, but it's different with Shar - and probably Selune, who is also heavily featured.
You can ask Shadowheart about Shar worshipping later, but that is after you have to react to her being a cleric of that goddess.

Last edited by fylimar; 23/10/21 04:36 AM.
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