One single concept you might want to know in advance because a lot of people seem to have trouble swallowing it:
The so called origin and end of everything. It's basically the nexus of all existence from which everything in the universe, including time and all alternate possibilities come from. It's literally everything: time, space, dimensions, life, etc. Everything comes from Akasha and everything goes to Akasha, and in the root is already all the information of how something is created, exists, and is eventually destroyed, so it is said that the point of origin and the point of end/death are actually the exact same thing.
That's likely the most complicated concept in the whole novel, so just chew on that for a while and you'll be fine.