That subtle Self is to be known by thought (ketas) there where breath has entered fivefold; for every thought of men is interwoven with the senses, and when thought is purified, then the Self arises.

In plain words: The subtle Self is known through the mind, here in the body where the breath works in five ways. People's thoughts are always tangled up with the senses. When the mind is made clear and pure, the Self shows itself.