At the age of 38, in August 1507, Guru Nanak Sahib heard God’s call to dedicate himself to the service of humanity after bathing in “Vain Nadi” (a small river) near Sultanpur Lodhi. The very first sentence which he ‘uttered’ then was, ‘There is no Hindu, no Musalman’. He now undertook long travels to ‘preach’ ‘his unique’
and divine doctrine (Sikhism). After visiting different places in Punjab, he decided to proceed in India and abroad. These tours are called Char Udasis of Guru Nanak Sahib. During the four journeys, Guru Nanak Sahib visited different religious places preaching Sikhism. He went to Kurukshetra, Haridwar, Joshi Math, Ritha Sahib, Gorakh Matta (Nanak Matta), Ayodhya, Prayag, Varanasi, Gaya, Patna, Dhubri and Gauhati in Assam, Dacca Puri, Cuttock, Rameshwaram, Ceylon, Bidar, Bharuch, Somnath, Dwarka, Junagadh, Ujjain, Ajmer, Mathura, Pakpattan, Talwandi, Lahore, Sultanpur, Bilaspur, Rawalsar, Jwalaji, Spiti Valley, Tibet, Ladakh, Kargil, Amarnath, Srinagar and Baramulla. Guru Nanak Devji also paid visit to Muslim holy places. In this regard he went to Mecca, Medina, Baghdad via Multan, Peshawar Sakhar, Son Miani, Hinglaj etc.
Some accounts say that Guru Sahib reached Mecca by sea route. Guru Devji also visited Syria, Turkey and Tehran (the present capital of Iran). From Tehran, Guru Devji set out on the caravan route and covered Kabul, Kandhar and Jalalabad. The real aim of his tour was awakening the people to realize the truth about God and to introduce Sikhism. He established a network of preaching centres of Sikhism which were called ‘Manji’s’. He appointed able and committed followers
as its head (preacher of Sikhism). The basic tenets of Sikhism were wilfully conceived by the people from all walks of life. The seeds of Sikhism were sown all over India and abroad in well-planned manner. In the year 1520, Babar attacked India. His troops slaughtered thousands of innocent civilians of all walks of life. Women and children were made captives and all their property looted at Amirabad. Guru Nanak Devji challenged this act of barbarity in strong words. He was
arrested and released, shortly after making Babar realizing his blunder. All the prisoners were also released
Guru Nanak Devji settled down at Kartarpur city (now in Pakistan) which was founded by him in 1522 and spent the rest of his life there (1522-1539). There was daily Kirtan and the institution of Langar (free kitchen) was introduced. Knowing that the end was drawing near, Guru Nanak Devji, after testing his two sons and some followers, installed Bhai Lehna Ji (Guru Angad Sahib) as the Second Nanak in 1539, and after a few days passed into Sachkhand on 22nd September, 1539. Thus ended the worldly journey of this god-gifted Master (Guru) of mankind. He rejected the path of renunciation Tyaga or Yogi, the authority of the Vedas and the Hindu caste system. Guru Nanak Devji emphasized the leading of householder’s life (Grihesta), unattached to gross materialism. The services of mankind Sewa, Kirtan, Satsang and faith in ‘one’ Omnipotent God are the basic concepts of Sikhism established by Guru Nanak Devji. Thus, he laid the foundations of Sikhism. He preached new idea of God as Supreme, Universal, all powerful and truthful. God is formless (Nirankar), the soul, the Creator, the self-existent, the incomprehensible and the Everlasting and the creator of all things (Karta Purakh). God is infinite, All-giver, Nirvair and Omnipotent. He is Satnam, the Eternal and Absolute truth.
As a social reformer Guru Nanak Devji upheld the cause of women, downtrodden and the poor. He attacked the citadel of caste system of Hindus and theocracy of Muslim rulers. He was a born poet. He wrote 947 hymns comprising Japji Sahib, Assa-Di-Var, Bara-Mah-Sidh-Gost, Onkar (Dakhani) and these were included in Guru
Granth Devji by Guru Nanak Devji. He was also a perfect musician. He with the company of Bhai Mardana composed such tunes in various Indian classical Ragas that charmed and tamed wild creatures like Babar, subdued Sagging kings, raved bigots and tyrants, made thugs and robbers saints. He was a reformer as well as a revolutionary. God had endowed him with a contemplative mind and pious disposition. Guru Arjan Sahib called him the image of God, nay, God Himself.