How does Chapter 45 describe the Guru's true nature, and what is the recommended way to meditate on him for spiritual progress?

Chapter 45 presents a profound view of the Guru's nature, stating that while Brahman is eternal and the world is transient, 'the Guru alone is the true Brahman.' The Guru is described as a 'solid mass of Brahman-consciousness.' Based on this understanding, the text outlines a specific method for spiritual advancement. The means to this goal is to renounce the transient world, which in turn gives birth to dispassion (Vairagya), and to meditate exclusively on the Guru. This constancy of feeling and focus on the Guru, who is the embodiment of the eternal Brahman, is the key. This practice ultimately leads to seeing divinity in all beings, a state referred to as 'undifferentiated worship' (Abheda-bhajan).