I’ll help expose the weaknesses in your signet so that when you come up against a dark wielder with such a power, you will have already practiced how to defeat them. Each of you has something to learn, and I’m here to keep you safe while you do it.”
I think Xaden is being used as a sort of spy for the Sage/Mavens to learn all the cadet's signets, strengths and weaknesses. Xaden is unaware.
