Pasupata Upanishad
Pasupatha means the way of the animal. It is the path by which the jivas (pasus) attain salvation. Pasupata Upanishad belongs to the Atharva Veda. It is a Saiva Upanishad, which envisions Lord Shiva as the supreme Brahman, the witness of everything and the impelling force behind all movements and actions. He is Pasupathi, the lord of the animals. This Upanishad is also called Pasupatabrahma or Pasupata Brahmana Upanishad.
The Upanishad is devoted to realizing one's true nature as soul. Shiva is the source of all knowledge and learning. He is impeller of the organs in the body. The outer form of learning has limitations since the senses and the mind cannot reach Para Brahman. Even the transcendental knowledge of sruti, what is heard, reaches us because of him only.