The thing I don't get about the recreance is why did they leave like that?
I'm pretty sure the Recreance is the betrayal that Jasnah mentioned. Seems obvious. What I don't understand is why? The feeling I got as I read that part was that the KR gave up on humankind for whatever reason, but even then it seems odd that they should give up like they did.
Let's say that they were somehow betrayed by the kings/humankind/whatever and gave up their shards in protest:
1. There is clearly a deep bond between the knight and the spren. If the shards are linked to the spren and the knights knew of it (and I can't imagine how they could not know) I don't see why they'd betray the sprean just because they themselves were somehow betrayed by the rest of mankind. Doesn't make sense.
2. Considering the enormous power of the shards, if their use was somehow linked to bringing about the desolations destroying or hiding them would be the reasonable thing to do.
Considering the above I think that the KR were somehow betrayed by both humankind AND "sprenkind" as well. They gave up their shards in protest against both. The why I cannot fathom.
If we remember that according to Jasnah the spren have complex organized societies and a high level of sentience, perhaps they're not perfect little creatures incapable of doing harm. They may have their own interests, and it may happen that those interests collided with humankind's after the last desolation.
What happened may have been kind of like when a friend of yours cheats on another friend of yours and you know about it. Whatever you say or do may be seen as a betrayal by either (or both) sides.
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