Truth...? In a way, I suppose. He told what he knew of the truth when I confronted him, and was one of those at my side when we uncovered a deeply hidden truth of the past. But the seat of Emet-Selch was that which oversaw what was once called the "Underworld". We'd call it the aetherial sea today - but he was a sorcerer of immense power and command over aether, and could even see and discern the color of souls. And...for those he cared for most, he could recognize those souls on sight, even if they were much diminished.

[It's clearly how he, Elidibus, and Lahabrea were able to awaken the shards of other Convocation members, even if they were only a glimmer compared to their original 'complete' shine. How could they have found them if he didn't know who he was looking for?]