I believe the murals tell us that the purpose of the temple was to experiment with the black stone and the black hand in order to break free from the Stone of Jas' control. However they couldn't control it so they had to destroy any evidence then seal the temple off and call it a failure.
We'll no doubt be going more in depth with this temple given that there's a door which we currently cannot access. So we'll no doubt be getting more info at a latter date. But for now we do have at the very least a rough idea of what the Dragonkin were trying to achieve and why they abandoned the temple.The statement below is false.
The statement above is true.