Why has the manas existed since beginningless kalpas?

Since beginningless kalpas, there have been two dharmas that are not born from causes and conditions. One is the eighth consciousness, the tathāgatagarbha, which exists originally and does not need to be born from any dharma. The other is the manas, the seventh consciousness, which also exists originally together with the eighth consciousness; it is not a dharma born later, nor is it born by the eighth consciousness through any conditions. However, the manas is still a conditioned, arising-and-ceasing dharma, not a real dharma; it requires the eighth consciousness to continuously output seeds of consciousness in order to maintain its existence, and it requires the eighth consciousness's continuous appropriation (upādāna) in order to exist.

Why is it that the manas, which has existed since before beginningless kalpas and is not born from causes and conditions, still belongs to the category of arising-and-ceasing, mutable dharmas? Because the manas has inherently possessed ignorance (avidyā) since before beginningless kalpas—especially the fundamental ignorance of the afflictions of greed, hatred, and delusion—and does not know that it itself is illusory. Therefore, its self-view (ātma-dṛṣṭi) and self-grasping cannot eliminate themselves, and it coexists with the eighth consciousness without disappearing. Once the manas completely severs the fundamental ignorance, self-grasping will be completely severed, and it will inevitably disappear, leaving only the eighth consciousness existing alone—without form or appearance, without clamor or disturbance, in tranquil nirvāṇa.