After the two sides reached a ceasefire agreement, Be'lakor told Aaron two stories about unlocking Tzeentch's power and Nurgle's power. He said they might offer Aaron some inspiration for unlocking his final Chaos power.
First, in an age when the 40K universe was not yet so dark, so deep, or so fantastical, before Slaanesh was born-although Slaanesh's subsequent birth caused Slaanesh to exist in every timeline within the Warp-the strongest of the Chaos Gods was not Khorne, but Tzeentch.
Tzeentch represented the power of change, and the universe's prevailing themes at the time were not slaughter, but progress, exploration, and transformation. Thus, Tzeentch became the most powerful of the Chaos Gods.
At the time, Tzeentch possessed a multiverse-level staff formed from a "concept"-the Nameless Staff. It was said that, with this staff, Tzeentch held the true names of all Chaos Daemons and possessed the "right to define" all creatures and concepts.
This was what it meant for one's words to carry absolute authority: if Tzeentch said something was so, then it was so, even if it was not. If Tzeentch said something could not be done, then it could not be done, even if it could.
The other Three Chaos Gods feared Tzeentch for this reason. After conferring, the Three Gods decided to join forces against Tzeentch. Khorne forged a greataxe capable of breaking every magical barrier, Nurgle brewed a thick soup capable of corrupting any terrain, and Slaanesh fashioned a rapier capable of piercing all armor. The Three Gods decided to deal Tzeentch a devastating blow.
After learning of this, the Lord of Change voluntarily destroyed the Nameless Staff. As a result, Tzeentch's strength fell from first among the Four Gods to third. Many could not understand this choice, but Be'lakor, the first Original Daemon Prince, glimpsed the truth