Mental Armament allows telepaths to wield their mental probes as weapons. They can transform their mental probe into defensive weapons to protect the mind or transform it into offensive weapons for attacking the minds of others.
Mental Armament is the first offensive means that telepaths gain. Not only is it powerful, it is also invisible. An enemy's mind can be stabbed without them knowing what happened.
So Gerald protected his mind from them. If they wanted to read his mind, they would need to break the shield created with his divine ability.
They didn't do that because they weren't hell-bent on antagonizing him and because they didn't have the tools to do so.
They have about the same spiritual power as he does, but Mental Probe is just not equipped for damaging the minds of others, so it will fail when it clashes against the Mental Armament divine ability.
