Oof I've been trying to get at the themes so bad with my first novel, Fireburnt, but I've been concentrating so badly on the technicalities, that I'm not sure I get there all the way. I'm already 81k into this story, and trying to figure out how to put everything I want into this without the story being longwinded.
SPOILERS?? if anyone cares haha, but in some sense of it, my motifs of water and fire are associated with the peace, healing, forgetting, love vs anger, hurting, remembering and hate respectively. One of my themes is about the necessity of the duality as well as the futility. We require both to be whole, as these are markers of who we were as we transform and grow in our lives. At the same time, that's all they are--markers. They don't decide our future or what we choose to do. We are always changing in that sense.
Others deal with the relationship between innocence, forgiveness, and choices.
There's probably a lot more because I like to think every story has a ton you just don't realize about, but these are the ones I think most of.