When the Acolytes first saw Van Buren, he was shrouded in shadows and appeared to have a deeply glowing eye of both red and blue. The source of the glow was unclear.
Throne Agent Thoros knows little about Van Buren, but intimated that Van Buren was not even present at the first meeting, and that what they saw was a psykic emanation. From this, the Acolytes realize that Van Buren is likely a powerful psyker.
If the Acolytes are successful in their missions, they may earn more trust from their Inquisitor. This could lead to additional rewards, responsibilities, and knowledge.