Swami Vivekananda was a great teacher of the Vedas and Vedic thought, and of the Upanishads in particular. His lecture on the Vedanta (Lahore, 1897) outlined several key concepts of Hinduism and clarified a lot of misconceptions regarding the Vedas and the Upanishads.
The theme of the Upanishads can be viewed as an attempt to find an ultimate unity among all things. “Knowledge is nothing but finding unity in the midst of diversity”. The goal of the Upanishads is to find unity in the midst of infinite variation in “this marvelously diversified universe, where prevail infinitely different names and forms, in matter and spirit – each thought differing from every other thought, each form differing from every other form”.