I did a lot of thinking about the format of epic fantasy while reading this book. (Sorry for the essay)
Sanderson is notorious for many things, and big books is definitely one of those! But truly, he has found a way to explore, over the course of so many different books and series the ultimate fate of beliefs themselves. Epic fantasy gives you the legroom to really explore these things and walk the reader through them, and the Cosmere is something even more special in that regard. I think that the Cosmere and each story contained within it is the perfect stage to discuss something as nebulous and as particular as impermanence (the idea that nothing stays the same forever). When nothing can stay the same forever, even godhood, it becomes that much more fascinating to think about the Cosmere on a bigger scale. Entire religions spring up in the span of a chapter in this WaT, and the theology of Sanderson's characters warp and change with the time. A fascinating demonstration of a real-life phenomena.
Adonalsium seems to have left the Singers with a promise and a task, but the faith in that promise wanes naturally over time and is eventually forgotten. Not intentionally, of course, but this is the ultimate fate of most theology. It is why Sazed's determination to keep as many religions as he possibly can is so interesting. The further away from a moment of creation or of godly action a people moves in terms of time, the more diluted that memory becomes. In the Cosmere as a whole, and definitely in Mistborn era 1 and SA arc 1, there seems to be an old guard and a young scrappy group of mortals (more or less) that pushes back and we get to SEE the results of that strife. Each era of Mistborn that we get to see is an expansion of the future that those scrappy mortals created, and it is so interesting to think about how the scrappy mortals may just turn into the enemy themselves given enough time and pressure on a Cosmological scale. Epic fantasy is a very special genre for this reason--the long form of its storytelling increases the emotional buy-in of its readers.
The truly incredible part is that Sanderson is also able to weave fantastic, emotionally gripping, stories and characters in between these huge plotlines. Moreover, the stories are not merely the same beginning, middle, and end for each iteration of the powers-that-be in Roshar or within the Cosmere overall. Each time the story changes, the power in that story changes. Each time the power changes hands, the way that that power is used and interpreted changes with it. Adonalsium went from one to several, and so naturally the Cosmere itself will be different. The power had no one to act through for thousands of years, naturally the way that that power works will be different. This means that the mysteries in one's stories can be that much more mysterious and engaging.
Even though there were things that, thanks to the WoBs and forums in general) we knew ahead of time, Sanderson still managed to keep the surprises coming. I suspect he thought for a long time about what to do about people guessing the Chana Davar thing waaaaaay early. Surely he wouldn't just not use that part of the story, but how much attention did he really need to give it in a book with more story than it logistically may have had the real estate for? I thought he handled that situation well. He gave it the weight that a reader who does not lurk on forums like these would expect for a discovery that big--while also keeping it tight. I am sure that there will be much more to come from that story, but the reader has their confirmation for the time being.
It's just a really interesting, detailed and long form, demonstration of the fact that nothing is permanent. Not people, or gods, or beliefs, or laws... Not even spren, despite being little pieces of divinity, are guaranteed to survive forever. Impermanence has been kind of a comfort for me in troubling times, and to see its assurance displayed so perfectly in the form of story is just that much more soothing. It's a very scary thing, but it's also a very comforting thing. You may not be warm now, but you will be warm again. I promise.
