I was listening to an interesting recording of a retreat that Ken McLeod led a couple of years ago. Ken McCleod is an American Buddhist teacher, who studied under Kalu Rinpoche and has done 2 traditional 3 year retreats. He said one time, he was with his friend Jack Kornfield. Kornfield is another influential Buddhist teacher that has spent time as a monk in Thailand, Burma, and India.
Jack asked Ken, “What is the main difference between Mahayana and Theravada?” Many would find that to be a loaded question and some could find many philosophical differences. Ken thought about it, and he replied space. In the Mahayana tradition, the doctrine of emptiness is related to space. When everything is negated, all that is left is a space like emptiness. Jack replied that it was interesting, because Ajahn Chah was his only teacher that ever talked about space.
Ken says that when he’s read Ajahn Chah’s books, there’s constant talk about space. He says what Ajahn Chah says is no different from what a Tibetan Mahamudra master would say, it’s basically identical. Within many traditions of Tibetan Buddhism, full realization of Mahamudra is the pinnacle of practice.
Ken said that type of understanding comes from the “maturation of practice.”