Through their tapas, the rishis acquired the supreme knowledge related to all these queries. The rishis of yonder started thirsting for better spiritual knowledge through deep meditation, they inquired into the cause of birth, death, jiva (soul), God, how God is related to soul, what is the true nature of living and non-living beings, human mind, intellect, ego, the connection between the creation and the creator (God) and so on. Desires don’t seem to get satiated, expectations are not always met and dissatisfaction still remains in life. Vedic procedures were too many, disciplines were too demanding, material needs to conduct rites were imposing and there could be so many lapses leading to failure of the intended purposes of conducting yagas. Having understood the benefits as well as the limitations of totally relying on vedic karmas, there were indeed such doubts and questions in the minds of the rishis. But, by doing the rites and fulfilling the worldly desires, several questions also came in the minds of rishis - are they really fulfilling? Are they able to solve all problems? Why wants, suffering, sorrows and pains in life do not seem to get eradicated totally from life simply through the path of conducting vedic rites? Is there some Supreme Truth behind the celestial Gods who are pleased by Vedic ceremonies and other Gods (Eswaras) of creation, sustenance and destruction? The earlier Karma Kanda part of Vedas was essentially to do with hymns, prayers, rituals and rites to please the celestial Gods for getting worldly life with desires and wants fulfilled. Why Jnana Kanda (Upanishads) considered the Ultimate of Vedic knowledge? It also said to mean the knowledge of Self/ Brahman (Atma Vidya/ Brahma Vidya). The word Upanishad in Sanskrit means “sitting down by the side” which actually relates to hearing the teachings of the saint by sitting close to him. Upanishads contain the core spiritual teaching of Vedas and are taught by Rishis to their deserving and spiritually earnest disciples in seclusion. The second, ending portions called the Gnana Kanda are the Upanishads that contain the quintessence of Vedic spiritual knowledge about God – Jnana. The Karma kandas are the first part of Vedas and they contain hymns, procedures and instructions regarding rites and ceremonies, rules of conduct and mantras and verses with intonations etc connected with doing Vedic karmas and fire ceremonies. The contents of each Veda are classified into two portions – the Karma Kanda and the Gnyana Kanda. They are also known as Aranyakas, that which were taught at forests.
Upanishads are the concluding parts of the four Vedas (Rig, Yajur, Sama and Atharva Vedas) they are also known as Vedantas (Veda+anta = end of Vedas).