"What do you mean?" Aksai frowned, trying to process her words.
Yelia took a deep breath before explaining.
"I'm sure you know this, but let me remind you anyway. This Demon Tree acts as a conduit for the corrupted druid's cultivation technique. It allowed him to use people's negative emotions as fuel to further his cultivation.
When the people trapped inside the Devil's Den felt anger, helplessness, and despair, the corrupted druid harvested those emotions with the Demon Tree's help. The Devil's Den was a necessary isolation barrier, designed to cultivate those emotions.
It not only added to the trapped people's misery but also helped the corrupted druid amass negative emotions and use them to refine his Spirit essence more easily. Every component in that incident was aimed at helping the corrupted druid achieve his breakthrough into the Foundation Building realm.