Answer by taking a quote from the following article:

Swami Vivekananda (Bengali: [Sami bibekanondo] ( listen); 12 January 1863 - 4 July 1902), born Narendranath Datta (Bengali: [norendronath doto]), was an Indian Hindu monk, a chief disciple of the 19th-century Indian mystic Ramakrishna.  He was a key figure in the introduction of the Indian philosophies of Vedanta and Yoga to the Western world and is credited with raising interfaith awareness, bringing Hinduism to the status of a major world religion during the late 19th century. He was a major force in the revival of Hinduism in India, and contributed to the concept of nationalism in colonial India. Vivekananda founded the Ramakrishna Math and the Ramakrishna Mission.

Vivekananda propagated that the essence of Hinduism was best expressed in Adi Shankara's Advaita Vedanta philosophy. Nevertheless, following Ramakrishna, and in contrast to Advaita Vedanta, Vivekananda believed that the Absolute is both immanent and transcendent. According to Anil Sooklal, Vivekananda's neo-Advaita "reconciles Dvaita or dualism and Advaita or non-dualism". Vivekananda summarised the Vedanta as follows, giving it a modern and Universalistic interpretation:  Each soul is potentially divine. The goal is to manifest this Divinity within by controlling nature, external and internal. Do this either by work, or worship, or mental discipline, or philosophy--by one, or more, or all of these--and be free. This is the whole of religion. Doctrines, or dogmas, or rituals, or books, or temples, or forms, are but secondary details.  Nationalism was a prominent theme in Vivekananda's thought. He believed that a country's future depends on its people, and his teachings focused on human development. He wanted "to set in motion a machinery which will bring noblest ideas to the doorstep of even the poorest and the meanest".  Vivekananda linked morality with control of the mind, seeing truth, purity and unselfishness as traits which strengthened it. He advised his followers to be holy, unselfish and to have shraddha (faith). Vivekananda supported brahmacharya (celibacy), believing it the source of his physical and mental stamina and eloquence. He emphasised that success was an outcome of focused thought and action; in his lectures on Raja Yoga he said, "Take up one idea. Make that one idea your life - think of it, dream of it, live on that idea. Let the brain, muscles, nerves, every part of your body, be full of that idea, and just leave every other idea alone. This is the way to success, that is the way great spiritual giants are produced".

Did he have any lectures?
Vivekananda propagated that the essence of Hinduism was best expressed in Adi Shankara's Advaita Vedanta philosophy.