Bulaya Boli Khasam Ka - "I say only what the Lord tells me." - All the Guru Sahebs put forth soul-stirring examples of Humility and did not take credit for anything. Dharam asked for "Roop" (form)from the Lord for its establishment, and How Guru Arjan Patshah gave the form of Nirankar to Sri Guru Granth Sahib. Guru Nanak Sahib Himself, in Sri Guru Granth Sahib, proclaim that The Lord Himself has taken the form of Sri Guru Granth Sahib - Waho "Waho Bani Nirankar Hai".
Amrit Bani (Gurbani) was the Guru from the very beginning, Sri Guru Nanak Sahib illuminated the world through Gurbani. The same Divine Jot continued the process of illumination through Gurbani in the Luminous Form of Sri Guru Angad Sahib. Sri Guru Nanak Sahib continued the Divine process through Sri Guru Amar Das Ji and so on. Illumination continues unabated-through the same Gurbani from Sri Guru Granth Sahib. For Gurmukhs, the eternal illumination is flowing straight from the holy lips of Jot Roop Har Guru Nanak where as others only perceive a holy book in front.