In the regimented society of a Humakt temple/military unit, I see God Talkers as Lieutenants filling the rank structure between Sergeants (Initiates) and Captain Runelords. As an Ex military guy it makes perfect sense. They would mainly take care of anything the Captain doesn't want to deal with. Captains are important men and cant be bothered with spending a week doing spell training for one warrior. Do you want the Captain of the Guard teaching First Aid to the new guys or guarding...who ever boss man is?
Well that is my take anyway.