The Upanishads
The Upanishads contain the essence of the Vedas. They are the concluding portions of the Vedas and are the source of the Vedanta philosophy. Profound, original, lofty and sublime thoughts arise from every verse. They contain the direct spiritual experiences or revelations of seers, or sages, the Rishis. They are the products of the highest wisdom, supreme divine knowledge. Hence they stir the hearts of people and inspire them.
Upanishads – Shukla Yajur Veda
Upanishads – Krishna Yajur Veda