Luli Venerable is one of the three fundamental incarnations of the Medicine Buddha, symbolizing his dignity as projected to the world outside.
In other words, Luli Venerable's status is neither too high nor too low, just right. Suppressing him in Buddha Hell can deter the other Bodhisattvas and Arhats.
Even the Buddhas of lower status would be intimidated by Buddha Hell, preventing them from entertaining other ideas.
Moreover, Buddha Hell, although protected by saints' Divine Ability, still has a lot of room for improvement. Now that Luli Venerable is captured, Jiang Chen intends to incorporate him in Buddha Hell, transforming it into a Divine Artifact.
In this way, even if Jiang Chen is not in Xiniuhe Continent, Buddha Hell is still capable of exercising its entire power, sufficient to suppress the Innate Dao Sovereign.
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