What does Baba describe as the ultimate purifier on the spiritual path, and how does one achieve it?

In Chapter 50, it is clearly stated that while holy places and vows are purifying, "knowledge is more purifying than the purifiers." This supreme purifier is Brahman-knowledge. The path to achieving it, however, begins with devotion. The text emphasizes that the mind is soiled by Avidya (ignorance) and its cleansing "cannot happen without devotion to God." Therefore, devotion is the critical first step that removes ignorance and allows knowledge to be born. This process is likened to a knowledge-sacrifice where ignorance is burned away, revealing the non-dual truth that one is Brahman, which is the ultimate state of purity.