In 1879, Narendra entered the Presidency College, Calcutta for higher studies. After one year, he joined the Scottish Church College, Calcutta and studied philosophy. During the course, he studied western logic, western philosophy and history of European nations.
Questions started to arise in young Narendra's mind about God and the presence of God. This made him associate with the Brahmo Samaj, an important religious movement of the time, led by Keshub Chunder Sen. And along with his classmate and friend Brajendra Nath Seal, he regularly attended meetings of the breakaway Sadharan Brahmo Samaj. Later they would part ways with Dutta aligning himself with Keshub Chunder Sen's Nava Vidhan and Seal staying on as an initiated member. During this time spent together, both Dutta and Seal sought to understand the intricacies of faith, progress and spiritual insight into the works of John Stuart Mill, Auguste Comte, Herbert Spencer and G.W.F. Hegel.
But the Samaj's congregational prayers and devotional songs could not satisfy Narendra's zeal to realize God. He would ask leaders of the Brahmo Samaj whether they have seen God, but their answers did not satisfy his quest for knowledge. It was during this time that Reverend William Hastie, the Principal of the Scottish Church College, told him about Sri Ramakrishna of Dakshineswar.
Though Narendra could not accept Ramakrishna and his visions, he could not neglect him either. It had always been in Narendra's nature to test something thoroughly before he would accept it. He tested Ramakrishna to the maximum, but the master was patient, forgiving, humorous, and full of love. He never asked Narendra to abandon reason, and he faced all of Narendra's arguments and examinations with patience. In time, Narendra accepted Ramakrishna, and when he accepted, his acceptance was whole-hearted. While Ramakrishna predominantly taught duality and Bhakti to his other disciples, he taught Narendra the Advaita Vedanta, the philosophy of Sankara.
During the course of five years of his training under Ramakrishna, Narendra was transformed from a restless, puzzled, impatient youth to a mature man who was ready to renounce everything for the sake of God-realization. In August 1886, Ramakrishna's end came in the form of throat cancer.When Ramakrishna was on his death bed,Vivekananda was on his side and thought "Are you the spirit even now?".Ramakrishna decalred,"He who was Rama and He who was Krishna is now RamaKrishna in this body". After this Narendra and a core group of Ramakrishna's disciples took vows to become monks and renounce everything, and started living in a supposedly haunted house in Baranagore. They took alms to satisfy their hunger and their other needs were taken care of by Ramakrishna's richer householder disciples.
Soon, the young monk of Baranagore wanted to live the life of a wandering monk with rags and a begging bowl and no other possessions. In July 1890, Vivekananda set out for a long journey, without knowing where the journey would take him. The journey that followed took him to the length and breadth of the Indian subcontinent. During these days, Vivekananda assumed various names like Vividishananda (in Sanskrit, Vividisha means "the desire to know" and Ananda means "bliss"), Satchidananda, etc. It is said that the Maharaja of Khetri, Ajit Singh, suggested to him the name Vivekananda because of his discernment of things, good and bad. Viveka or discrimination between the eternal and the transient was highly valued by the Swami, who, recollecting that Keshab Chandra Sen used to call him by that name, accepted it.
During these wandering days, Vivekananda stayed in kings' palaces, as well as the huts of the poor. He came in close contact with the culture of different regions of India and various classes of people in India. Vivekananda observed the imbalance in society and tyranny in the name of caste. He realized the need for a national rejuvenation if India was to survive at all. He reached Kanyakumari, the southernmost tip of the Indian subcontinent, on 24 December 1892. There, he swam across the sea and started meditating on a lone rock. He thus meditated for three days and said later that he meditated about the past, present and future of India. The rock went on to become the Vivekananda memorial at Kanyakumari.
Vivekananda went to Madras and spoke about his plans for India and Hinduism to the young men of Madras. They were impressed by the monk and urged him to go to the United States and represent Hinduism in the World Parliament of Religions. The Raja of Ramnad, who was originally invited for the conference, promoted Vivekananda as the right person to represent the views of Hinduism in the Parliament. Thus, helped by his friends at Chennai, Bhaskara Sethupathi, Raja of Ramnad and Maharajas of Mysore and Khetri, Vivekananda set out on his journey to the USA.
In one of his lectures in California, the swami described about his condition during wandering days as follows:
Many times I have been in the jaws of death, starving, footsore, and weary; for days and days I had no food, and often could walk no farther; I would sink down under a tree, and life would seem to be ebbing away. I could not speak, I could scarcely think, but at last the mind reverted to the idea: "I have no fear nor death; never was I born, never did I die; I never hunger or thirst. I am It! I am It! The whole of nature cannot crush me; it is my servant. Assert thy strength, thou Lord of lords and God of gods! Regain thy lost empire! Arise and walk and stop not!" And I would rise up, reinvigorated; and here I am today, living! Thus, whenever darkness comes, assert the reality and everything adverse must vanish. For after all, it is but a dream. Mountain-high though the difficulties appear, terrible and gloomy though all things seem, they are but Maya. Fear not, and it is banished. Crush it, and it vanishes. Stamp upon it, and it dies.
Vivekananda was encouraged by J.H. Wright, a professor of Greek at Harvard University, to represent Hinduism in the 1893 World Parliament of Religions in Chicago. When he expressed reservations saying he had no credentials, the professor replied, "To ask you, Swami, for your credentials is like asking the sun about its right to shine." He wrote about Vivekananda to the chairman of the committee on selection of delegates, "Here is a man more learned than all our learned professors put together."
Vivekananda was received well at the Parliament of Religions, where he delivered a series of lectures. The audience arose in their seats and applauded loudly (for two minutes) when he started his first address with the famous words, "Sisters and brothers of America." When the applause subsided the Swami began his speech by thanking the young nation "in the name of the most ancient monastic order in the world, the Vedic order of sannyasins. A newspaper account described him as "an orator by divine right and undoubtedly the greatest figure at the Parliament." Vivekananda's arrival in the USA has been identified by many to mark the beginning of western interest in Hinduism not as merely an exotic eastern oddity, but as a vital religious and philosophical tradition that might actually have something important to teach the West.
Vivekananda successfully introduced yoga and Vedanta to the West and lectured around America introducing the topics (1894-6). He taught hundreds of students privately in free classes held in his own room beginning in New York in 1895. Later, he started Vedantic centers in New York City and London, lectured at major universities and generally kindled western interest in Hinduism. His success was not without controversy, much of it from Christian missionaries of whom he was fiercely critical. After four years of constant touring, lecturing and retreats in the West, he came back to India in the year 1897.
However, he had to bear great criticism from other orthodox Hindus for having traveled in the West. In his day there was hardly a Hindu in America and he received criticism for crossing the ocean, at that time a cause for "outcasting." Vivekananda scoffed at these critiques from the orthodox, saying "I cannot be outcast - As a monk, I am beyond caste." His contemporaries also questioned his motives, wondering whether the fame and glory of his Hindu evangelism compromised his original monastic vows. His enthusiasm for America and Britain, and his spiritual devotion to his motherland, caused significant tension in his last years.
He once again toured the West from January 1899 to December 1900. He inculcated a spirit of respect and goodwill for exchanges between the East and the West. He had American disciples whom he brought to India and initiated as Swamis and brought Indian Swamis to America where they and their successors have been ever since.
Swami Vivekananda belonged to that branch of Vedanta that held that no one can be truly free until all of us are. Even the desire for personal salvation has to be given up, and only tireless work for the salvation of others is the true mark of the enlightened person. He founded the Sri Ramakrishna Math and Mission on the principle of Atmano Mokshartham Jagad-hitaya cha (आत्मनॊ मोक्षार्थम् जगद्धिताय च) (for one's own salvation and for the welfare of the World).
However, Vivekananda also pleaded for a strict separation between religion and government ("church and state") a value found in Freemasonry which as a Freemason he had been exposed to. Although social customs had been formed in the past with religious sanction, it was not now the business of religion to interfere with matters such as marriage, inheritance and so on. The ideal society would be a mixture of Brahmin knowledge, Kshatriya culture, Vaisya efficiency and the egalitarian Shudra ethos. Domination by any one led to different sorts of lopsided societies. Vivekananda did not feel that religion, nor, any force for that matter, should be used forcefully to bring about an ideal society, since this was something that would evolve naturally by individualistic change when the conditions were right.
Vivekananda made a strict demarcation between the two classes of Hindu scriptures : the Sruti and the Smritis. The Sruti, by which is meant the Vedas, consist of eternally and universally valid spiritual truths. The Smritis on the other hand, are the dos and donts of religions, applicable to society and subject to revision from time to time. Vivekananda felt that existing Hindu smritis had to be revised for modern times. But the Srutis of course are eternal - they may only be re-interpreted.
Vivekananda advised his followers to be holy, unselfish and have shraddha (faith). He encouraged the practise of Brahmacharya (Celibacy). In one of the conversations with his childhood friend Sri Priya Nath Sinha he attributes his physical and mental strengths, eloquence to the practice of Brahmacharya.
Vivekananda didn't advocate the emerging area of parapsychology, astrology (one instance can be found in his speech Man the Maker of his Destiny, Complete-Works, Volume 8, Notes of Class Talks and Lectures) saying that this form of curiosity doesn't help in spiritual progress but actually hinders it.
Swami Vivekananda is widely considered to have inspired India's freedom struggle movement. His writings inspired a whole generation of freedom fighters including Aurobindo Ghose and Bagha Jatin. Vivekananda was the brother of the extremist revolutionary, Bhupendranath Dutta. Subhash Chandra Bose one of the most prominent figures in Indian independence movement said,
Vivekananda inspired Jamshedji Tata to set up Indian Institute of Science, one of India's finest Institutions. Abroad, he had some interactions with Max Mueller. Nikola Tesla was one of those influenced by the Vedic philosophy teachings of the Swami Vivekananda.
Above all Swami Vivekananda helped restore a sense of pride amongst the Hindus, presenting the ancient teachings of India in its purest form to a Western audience, free from the propaganda spread by British colonial administrators and Christian missionaries, of Hinduism being a caste-ridden, misogynistic idolatrous faith. Indeed his early foray into the West would set the path for subsequent Indian religious teachers to make their own marks on the world, as well herald the entry of Hindus and their religious traditions into the Western world.
Swami Vivekananda's ideas have had a great influence on the Indian youth. In many institutes, students have come together and formed organizations meant for promoting discussion of spiritual ideas and the practice of such high principles. Many of such organizations have adopted the name Vivekananda Study Circle. One such group also exists at IIT Madras and is popularly known as (VSC) Additionally, Swami Vivekananda's ideas and teachings have carried on globally, being practiced in institutions all over the world.
However, Vivekananda himself says in the book,
It is not the sign of a candid and scientific mind to throw overboard anything without proper investigation. Surface scientists, unable to explain the various extraordinary mental phenomena, strive to ignore their very existence.
He further says in the introduction of the book that one should take up the practice and verify these things for themselves, and that there should not be blind belief.
What little I know I will tell you. So far as I can reason it out I will do so, but as to what I do not know I will simply tell you what the books say. It is wrong to believe blindly. You must exercise your own reason and judgment; you must practise, and see whether these things happen or not. Just as you would take up any other science, exactly in the same manner you should take up this science for study.
The great electrical engineer, Nikola Tesla, after listening to Vivekananda's speech on Sankhya Philosophy, was much interested in its cosmogony and its rational theories of the Kalpas (cycles), Prana and Akasha. His notion based on the vedanta led him to think that matter is a manifestation of energy . After attending a lecture on vedanta by Vivekananda Tesla also concluded that, modern science can look for the solution of cosmological problems in Sankhya philosophy, and he could prove that mass can be reduced to potential energy mathematically.