Davis sensed Vereina also absorbed the Celestial Luminescence Pill's pill essence. He realized that he didn't need too much essence.
For one, this was practically an Immortal Emperor Grade Pill, so the Laws of that stage were still restricted to the Immortal King Stage even if he got insights at the Immortal Emperor Grade from it. It would be hard for him to comprehend them with natural restrictions imposed by the heavens, which meant that he would need to wait for the Celestial Luminescence Pill to restore its energy before absorbing it again when he finally steps into the Immortal Emperor Stage.