The most recited verses honouring the guru — who is Brahma, Vishnu and Maheshvara, and the very Supreme made visible — chanted before study, satsang and on Guru Purnima.
Yes. Tradition regards the guru-tattva — the guiding principle itself — as present in every genuine teacher, in the ishta devata, and in whatever removes one's darkness. The salutation honours that principle.
Source: Guru Gita (Skanda Purana). Regional versions may vary — this text follows the version most widely used in community worship.