Using the analogies from Chapter 17, can you explain the difference between Shreya and Preya?

Chapter 17 explains the concepts of Shreya and Preya through powerful analogies. They are first described as being as opposite as light and darkness, highlighting their fundamentally different natures. Shreya is the light of pure Knowledge (Vidya), while Preya is the darkness of Ignorance (Avidya). The text further illustrates this with a beautiful metaphor: just as water and milk can be mixed, so too are Shreya and Preya blended in life. However, a courageous and wise person, like a swan (Maral) at Manasarovar, is able to separate and partake only of the pure milk (Shreya), leaving the water (Preya) behind. This emphasizes the need for discrimination to choose the spiritual path over worldly attachments.