The Essence of Upanishads, the knowledge portions of Vedas

hinduwiki.com — Of the 120 or so Upanishads which are extant, about twelve are considered to be major Upanishads. Almost every religious teacher has commented on most of these major Upanishads. They are all discourses and dialogues on spiritual experiences and pursuits. They are expositions on fundamental questions transcending the day-to-day phenomenal realities