Based on the opening shlokas in the Introduction, how is the concept of the Sadguru defined and revered?

The Introduction in Chapter 0 begins with powerful traditional invocations that define the supreme nature of the Sadguru. The first shloka famously equates the Guru with the holy trinity, stating, 'The Guru is Brahma, the Guru is Vishnu, the Guru is Lord Maheshwara; the Guru is the manifest Supreme Brahman.' This establishes the Guru as the embodiment of the creative, preservative, and destructive aspects of God, and as the ultimate reality itself. The second shloka, as cited in Chapter 0, further elaborates on the Guru's qualities, describing him as 'the bliss of Brahman,' the bestower of supreme happiness, the personification of knowledge, beyond all duality, eternal, pure, immovable, and the 'witness of all intelligence.'