What ideas did the Upanishads develop?

The Upanishads developed key philosophical ideas central to Hinduism, including the concepts of Brahman and Atman, which represent the ultimate reality and the individual soul, respectively. They explore the nature of existence, the relationship between the self and the universe, and the pursuit of spiritual knowledge through meditation and introspection. The texts emphasize the importance of understanding one's true self as a means to achieve liberation (moksha) from the cycle of rebirth (samsara). Additionally, they introduce the idea of unity between the individual and the cosmic, advocating for a deeper comprehension of existence beyond the material world.