Every sentient being is capable of attainting enlightenment, which is not so much a change from one extreme, Samsara, to another, Nirvana, but the ineffable experience in which both have ceased to dominate the thought of man so that he begins to live his life as transformed by pure transcendence. Samsara and Nirvana are not entities, but interpretations of our experiences, and as such are both Sunyata, which again is an operational term, not an ontological concept. Although all sentient beings may attain enlightenment by their own efforts, because each is a potential Buddha, human existence is the most suitable occasion for such striving. It is not something self-evident, although we can only act as human beings.
— from the introduction to Jewel Ornament of Liberation (translated by Herbert V. Guenther)
Gampopa Sonam Rinchen (1079–1153) was a Buddhist monk who established the Kagyu school, one of the four major schools of Tibetan Buddhism. A physician from Dagpo, Tibet, he was the star pupil of Tibetan Buddhist master Milarepa. Renowned for clarity of perception and knowledge of Buddhist practices, Gampopa wrote The Jewel Ornament of Liberation as a way to integrate various strands of Buddhist practices. This synthesis became the basis for various monasteries which he had founded.