A Catholic Benedictine monk, David Steindl-Rast, once explored the Tibetan Buddhism claimed that a person of high spiritual development could exit their physical body, vanish in mere days, leaving behind only ashes, to become a ‘rainbow body,’ of manifest light.
The Rainbow Body of Dzogchen
In Dzogchen, ‘rainbow body’ is a level of realization. Dzogchen is defined as the peak and most absolute path to enlightenment. That the decisive nature of all perceptive beings is pure, natural state of timeless clarity, which has no form of its own but is capable of seeing, undergoing, perceiving, or expressing all form, without being affected by those forms in any ultimate, permanent way.
The rainbow body however is not limited to Buddhism only it can be met in different traditions
The achievement of a ‘rainbow body’ is possible either shrinking the body before death or at the time of death or wholly transforming the body into light. Rainbow body through Dzogchen entails transforming the body into light and remain functional and visible through that light.
Twentieth-century practitioners of Dzogchen who have attained the Body of Light include the teachers and family members of Namkhai Norbu Rinpoche.
Padmasambhava or other name Guru Rinpoche was the first person to achieve this feat in the 8th-century. According to Buddhist history, he performed several miracles during his time. For example, he could fly, change a rock into sculpture with his mind, and leave his fingerprint or footprint in solid stone.
Visiting one of the memorials dedicated to him in Southern Asia you can allegedly see his marks of hand and foot still left in the stone.
When Padmasambhava died in his physical state his body was transformed completely back to its natural elements to leave nothing remaining. This lead to the creation of a new family of Buddhist educations, which was the start of what became the Nyingma tradition, which is the basis of Tibetan Buddhism known today.
Body of Light in different traditions
William Henry and Dr. Mark Gray reveal the widespread prevalence of light-body references in numerous ancient traditions—where the human body is transfigured into a new form.
In Sufism it is called “the most sacred body” and the “supracelestial body.” Taoists call it “the diamond body,” and those who have attained it are called “the immortals” and “the cloudwalkers.” Yogic schools and Tantrics call it “the divine body.” In Kriya yoga it is called “the body of bliss.” In Vedanta it is called “the superconductive body.” The ancient Egyptians called it “the luminous body or being” (akh) or the karast. This conception evolved into Gnosticism, where it is called “the radiant body.” In the Mithraic liturgy it was called “the perfect body.” In the Hermetic Corpus, it is called “the immortal body.” In the alchemical tradition, the Emerald Tablet calls it “the golden body.”
There is, in fact, quit a bit of postmortem research on this paranormal phenomenon in Tibet. Rast endeavored to research the death of a Tibetan Monk, Khenpo Achö, who had reportedly obtained rainbow body because he thought it could help him more deeply understand the resurrection of Jesus Christ, but his search was followed by many more inquiries, each researcher delving in for their own personal or spiritual reasons. Khenpo Achö attained the rainbow body on a hillside above Lumorap in September 1998. Regional press gave specific accounts of the process, and “The Rainbow Body,” appeared in an Institute of Noetic Sciences Review 59 (March–May 2002); it was also mentioned by Matthew T. Kapstein in The Presence of Light: Divine Radiance and Religious Experience(University of Chicago Press, 2004).
Khenpo Achö is of some notoriety, but so are others who have obtained rainbow body, like Bon po master, Sharrdza; thousands of yogis in the Tamil Siddha tradition and others, Christian saints like Peter Celestine, Sergius of Radonezh, and Seraphim of Sarov, along with numerous accounts from Taoist masters.