Let’s have a quick look at the 13 principal Upanishads:
Chandogya Upanishad
The Chandogya Upanishad is the Upanishad that belongs to the followers of the Sama Veda. It is actually the last eight chapters of the ten-chapter Chandogya Brahmana, and it emphasizes the importance of chanting the sacred Aum and recommends a religious life, which constitutes sacrifice, austerity, charity, and the study of the Vedas while living in the house of a guru. This Upanishad contains the doctrine of reincarnation as an ethical consequence of karma. It also lists and explains the value of human attributes like speech, will, thought, meditation, understanding, strength, memory, and hope.
Kena Upanishad
The Kena Upanishad derives its name from the word ‘Kena’, meaning ‘by whom’. It has four sections, the first two in verse and the other two in prose. The metrical portion deals with the Supreme Unqualified Brahman, the absolute principle underlying the world of phenomenon, and the prose part deals with the Supreme as God, ‘Isvara’. The Kena Upanishad concludes that austerity, restraint, and work are the foundation of the mystical doctrine; the Vedas are its limbs, and the truth is its home. The one who knows it strikes off evil and becomes established in the most excellent, infinite, heavenly world.
Aitareya Upanishad
The Aitareya Upanishad belongs to the Rig Veda. It is the purpose of this Upanishad to lead the mind of the sacrificer away from the outer ceremonial to its inner meaning. It deals with the genesis of the universe and the creation of life, the senses, the organs, and the organisms. It also tries to delve into the identity of the intelligence that allows us to see, speak, smell, hear, and know.
Kaushitaki Upanishad
The Kaushitaki Upanishad explores the question of whether there is an end to the cycle of reincarnation and upholds the supremacy of the soul (‘atman’), which is ultimately responsible for everything it experiences.