Fear is the Mind Killer
"Now, putting aside the topic of the Grimoire, there is nothing more precious in this room... probably... search through it; I am going to take a look at something on the outside."
Samiel stated as he stored the Grimoire Lux Brumalis in his Dimensional Ring while he went to the exit of the cave and looked at the peak of Snowrose Peak. When he was holding it, he knew that the Grimoire was not rejecting him, but such intelligent books would want to talk with him.
That was not the case with the Basic Principles of the Void Necrosis because Samiel, as Eldritch Creature, was practically the most excellent candidate, so the Grimoire automatically judged him as the most suitable host.
That was because of the natural affinity he had with it, which was the deciding factor when the Grimoire judged someone as suitable or worthy.