I personally believe that is comes from Wisdom. While the Acolytes are evil (or grossly misinformed) I believe that Cygnus has taught them to be wise. That is why Qudssi, with all his knowledge on man, helps him get mental resistance, he is naturally wise.
The reason I don't say intelligence is that nether Rahel or The Hero (if aptitude is high enough) get mental resistance...
The reason I don't say intelligence is that nether Rahel or The Hero (if aptitude is high enough) get mental resistance...