Guru Nanak, who appeared in this illusionary world in mid 15th century, was a great revolutionary as well as a reformist thinker. He established the Sikh institution through emphasizing on the concepts of Shabad Guru. His light (Nanak-Jyot) later through his successors taught the world the concept of humility, compassion, righteousness and service to the Guru. The concept of Shabad Guru and Shabad Brahm was prevalent since ancient times, but the importance...