[X] Preach to the Choir. Disputes over doctrine can lead to the most virulent of feuds, and you would rather have a thousand minds in broad agreement than a hundred locked in fanatic loyalty. Smooth over the divisions that lead to the call for the Hereticus, and the rest will fall smoothly into place.
A nice neat way to hold a sermon to reaffirm our doctrine while also swaying the entire planetary priesthood to our point of view? Yes please. Besides it's not like exposing the guilty would actually solve anything beyond getting rid of the people who were brave enough to contact outside forces to solve, what they saw, as dangerous views. I mean, just how many priests here don't actually believe in our views but went along with what they were told because they were too scared to make a move against their superiors or had so little faith they decided to just spout words they were told to say but felt no connection to them. This wouldn't get rid of the doubtful, it would just keep everyone in line with fear.
Igniting the soul has a similar issue as it seems to focus on our divinity rather then our message. If we do that then, well, none of the priests would actually believe in our doctrine. Sure they'd follow our message and preach our words but only because they were our words rather then because they have been converted to our way of thinking.
It's like.... following the words of the bible, not because you believe in them but rather because you respect the pope and the pope told you to follow the bible. You don't really believe in the bible you just believe in the pope. What we want is true believers, not fans.