Based on the provided text, what is the true, untainted nature of the Soul?

The text from Chapter 19 clarifies that the Soul is distinct from the body, senses, mind, and life-force. Its true nature is self-luminous, pure consciousness, changeless, and formless. To illustrate this, an analogy of a crystal is used: just as a crystal appears to take on the color of an object near it (like red or black) yet remains pure, colorless, and unchanged, the Soul remains untainted by the actions of Maya. Even though it appears in the world, it is fundamentally distinct from all worldly attributes and changes.