Olden says Hitler talked about it for days and was mesmerized by the lead character “who rouses the working masses by his speeches.”  The author points out that that was ten years before “he himself put the power of spoken word to the proof.”
According to Olden, Hitler spent days discussing a concept with fascination, particularly drawn to the lead character's ability to rally the working class through powerful speeches. This happened ten years prior to Hitler using his own voice to influence people.