। ॥ ५९८ ॥
In plain words
No one else can know him, and yet he knows the character of deep sleep firsthand. The one who, right there, knows that the intellect and all the rest are gone — that is the Self, and it never changes.
Close to the Sanskrit
Himself not being known by other people, he directly knows the attribute belonging to deep sleep; and who here is the knower of the absence of intellect and the rest — that, this indeed is the Self, free from change.