Gravis decided to use the emblem later. He wasn't really worried that the guy had some kind of trap in mind. After all, the guy was powerful enough to use a level six Law. Someone with that power wouldn't need to use any kind of scheme on Gravis.
Gravis was quite interested in this teacher that the Immortal Emperor talked about. This teacher obviously had to be an Immortal Emperor, at least. Usually, Gravis would have believed that this person wanted Gravis to join their Sect, but the things that the Immortal Emperor said made this improbable.
First of all, he said that his teacher didn't have any Sect. Second of all, he said that his teacher only searched for weak and lonely Cultivators.
When a normal Cultivator heard that claim, they might believe that this was due to an altruistic reason. After all, why else would someone only accept the weakest and loneliest souls into their midst?