It's one of the few "mystical" things left unexplained. Nothing we've seen other channelers do even comes close to that.

Think about it- an impenetrable barrier, so strong that apparently even the Forsaken couldn't touch it, that was keyed to the reincarnated soul of someone who had been long dead and would not reincarnate for thousands of years.


I also find it weird that it's flawed- obviously they knew how, in the AoL, to make non-flawed sa'angreal. The best argument I could think of would be making it flawed like that was necessary, because it would force Rand to act in certain ways he might otherwise not, but it's still weird. Plus, WoT doesn't really have that kind of prophecy manipulation that you see in other books, like Sword of Truth, for example.