I was also thinking that sorcery was akin to mathematics, as Wilshire pointed out. I read that quote as, basically, the Gnosis is the Meta-Anagogis, the refining, expanding principle inherent in sorcery taken to the next level (i.e., arithmetic vs. calculus or trig). Or maybe its artists (using imagery to show an effect) vs. scientists (using formulas to describe the effect).
There was a scene in the books (maybe TWP?) where Akka muses about Kelhus' potential as a Shaman, someone who uses sorcery and can heal like a prophet. Were Shamans prophets, or prophets Shamans? Could someone be a prophet without being a Shaman, or be a Shaman without being a prophet? Xinemus believed that prophets could heal, implying some supernatural ability (i.e., restoring sight to the blind). Maybe at some point there was a schism where Shamans ceased to exist, when Sorcerers and prophets became separate things. So, a Sorcerer would be a false prophet (speaking only the destructive words of God), whereas a prophet can only speak the restorative words of God (heal). Maybe Shamans were balanced and thus not damned. Begs the question: can Cishaurim heal?
Went on a tangent there.