Guru Nanak, in traditional stories, was raise a Hindu, but always questioned why the Hindu religion was so structured. He couldn't believe that some people were so easily swept into repeating senseless rituals, and he didn't like that ritualism gradually began to replace genuine faith. He also felt similarly toward Muslims, whom he felt were reducing their faith to mere repetition of the Qur'an and prayers.
One day, while bathing, he disappeared. He reappeared three days later claiming that there was no such thing as a Muslim or a Hindu. From that day forward, he began preaching a religion of One God, tolerance for all people, and dependence on faith alone rather than ritual and established religious traditions (such as fasting, formulaic prayers, pilgrimage, etc.).
He passed his "Guruship," which he obtained when he disappeared in the river, on to a successor, who then passed it on, and it went through ten Gurus before finally resting in the Sri Guru Granth Sahib. With each Guru the religion of Sikhism took on a more pronounced and distinct form, rendering itself independent of Sufism, Islam, Hinduism, or the Bhakti movement.
So, the mission of Sikhism is the mission of any other religion: to unite all peoples under a common understanding of the Divine. Guru Nanak's mission, however, was to simply teach people of a common God that is understood by different names and to make them realize the folly of organized religion. At least that's how I see it.
However men try to reach me, I return their love with my love; whatever path they may travel, it leads to me in the end - Bhagavad Gita 4:11
"Knowledge is a light which God casteth into the heart of whomsoever He willeth" - The Four Valleys; Hadith
आई पंथी सगल जमाती मनि जीतै जगु जीतु ॥ See the brotherhood of all mankind as the highest order of Yogis; conquer your own mind, and conquer the world.
आदेसु तिसै आदेसु ॥ I bow to Him, I humbly bow.
आदि अनीलु अनादि अनाहति जुगु जुगु एको वेसु ॥२८॥ The Primal One, the Pure Light, without beginning, without end. Throughout all the ages, He is One and the Same.
for his mission Guru Nanak travelled extensively , from Hindu temples , muslim mosques , himalayan yogis .
i will gave account of Guru sahibs travel ,heres first one
Guru Nanak Dev ji while on his eastward journey reached Haridwar. It is on the banks of the river Ganges and is one of the major centers for Hindu pilgrimage. The people, gathered there in large numbers, were bathing in the holy river. Guru Nanak Dev observed many people throwing water towards the sun in the east. The Guru had already heard about this meaningless ritual. He, therefore, thought it the right place and the proper time to give correct guidance that those kinds of mindless hollow rituals have no value. These people who throwing handfuls of water from river Ganges, towards the sun in the east, believed that by this ritual they could offer water to their dead elders in the next world. This next world was in the East from where the Sun rose. Guru Nanak Dev entered the river for purposes of bathing as other common pilgrims were doing. Instead of throwing water to the east, he, however, started throwing water in the opposite direction towards the west where Guru ji farm was. Taking him as a naive visitor, the nearby bathers told him that he was not performing the rituals correctly. They advised him to throw water to the east. Guru Nanak Dev continued throwing water towards the west pretending that he was very much absorbed in the 'holy' act and had not heard anything. Soon, many people gathered there to tell him that the proper method of performing the ritual was to throw water in the other direction. His water thrown to the west was of no use to him or to his dead ancestors. The pilgrims thought that the Guru was acting strangely and soon many hundreds of bathers surrounded him and were tell Guru ji that he was throwing the water in the wrong direction and that it will never get to his ancestors - who live in the East. They flocked to the Guru and laughed at what they thought was a very funny action. The leader of the pilgrims approached and asked Guru ji, “Why are you throwing the holy water to the West in the wrong direction?” By this time many thousand of bather were watching Guru ji. "The water is to be thrown towards the rising sun in the east so that it reaches your dead ancestors." The Guru calmly replied, “I am watering my withering crops in Punjab. All my crops in my village are dying as there has been no rain” and continued to splash the water to the west. He wanted to irrigate those crops. Hearing Guru ji reply the people started laughing. The curious spectators asked, “Are you crazy? How can your water reach hundreds of miles away to Punjab from here?” Guru ji replied, “The very same way as yours reaches your ancestors in the other world many millions of miles away. In fact, my farm is quite closer on this very earth." Guru ji stopped splashing the water. Guru ji became serious and asked, "If the water thrown by me cannot reach a few hundred miles away on this very earth, how can water thrown by you to your dead ancestors reach them in the heavens?" The leader of the pilgrims had no answer to this. The people became silent and started thinking over the reply given by the Guru. They had no logical argument to challenge his statement. This made the people think about the uselessness of their ritual. Guru Nanak Dev came out of the river and the crowd followed him. The Guru calmly told them the truth. He explained that hollow rituals do not have any religious value. They should love, respect and take care of their people, friends and religions when they are alive rather then perform these useless rituals afterward. When people die, they do not need anything from us and neither can we send them anything after they have left this world. After death, people get what they have given to the needy, out of their honest earnings, while living on this earth. So remember the message - Do the good deeds for your elders now - because once they are gone, you will not be able to do any service for them. Don't lose this opportunity! How effective and rational a way to get people’s attention and remove their ignorance!