I would say the most widespread theme is the general corruption of information over time, outlined in the first paragraph Chapter 1 of every book. But also reflected in the descriptions of news travelling about major events in the series, how the names and lyrics of songs change between different lands, and how our Age seems to be source of many of their myths, and their Age seems to be the source of ours.
I think responsibility is another theme of the series. How people react to it, interpret it, and interact with it. Perrin has an an exceptional sense of personal responsibility. He's constantly taking more on than he should. Meanwhile Matt sucks and avoids his responsibilities to the point he makes up a metaphor using boots without knowing what a metaphor is.
One of the ones we try to track in the chapter summaries is knowledge and information - how often people act on incomplete or incorrect information and how they reject new information because it doesn't conform to what they already think is true
I think an important theme is opposing but often complimentary forces:
Chaos (The Dark One) and Order (The Creator).
Selfishness (The Dark One) and Selflesness (the Creator).
Saidin and Saidar.
Chaotic Undirected Evil (The Dark One) and Controlled Directed Evil (Shadar Logoth/Padan Fain)
Honor and Duty.
Which I think emphasises a philosophy focusing around the importance of balance and how the best things can be achieved together (I think this is typified by the example of Circles - only with all component parts can the sum of the parts equal more than the whole.
cultural differences and how they can lead to missunderstandings, definantly a big one i would think with all the care he took to detail traditions and history for the different cultures, as well as ways of expresion, clothes and so on and forth. And a very relevant subject in todays world too.
I moved just within my own country several times in my life, and even within just my one country there are cultural differences, like how direct people are, whats considered polite and rude, how one express oneself with words - example: while one word can be an endeerment one place it can be seen as an insult another place...
I really REALLY recommend reading the new Origins of the Wheel of Time that came out last month. The author does a really good job picking out themes and working backwards to how RJ came about them/decided on how to use them.
It was also really nostalgic and made me tear up a couple of times