The Harrowing is a Prophecy and a Promise.
After Lun-Kheren lost many friends and children in a phyrric victory against the first tyrant, Kyzan, he screamed it the to the sky. At his coronation, the crowds shouted it back. It is carved into the armrests of the Four Sovereign Thrones.
Monoliths cannot be the only form of rule.
It is a reminder that the Monoliths can be killed. That the Meta can be snuffed out.