Based on Zimmermann's story [Figure; 152] it sounds that when Lewis recited the prayer that then the spirit was unleashed, made itself known, and began to annoy Lewis.
The only way out of this, I suppose, is to believe that Lewis’s wishes for protection and power were so great that the spirit “heard” his thoughts and led him down a path that would hopefully – for the sake of the spirit – actually awaken and free it. But if that were the case, I would suspect anyone who held the amulet and wanted “power” might get some sort of signs from the bottled spsirt, too. I dunno - perhaps it’s not the plot hole I think it is but something in this final explanation seems off.
We've put the question up in our forum for the rest of you to come over and figure in your thoughts on the matter.