The Heart Sutra is a well-known Mahāyāna Buddhist Sutra that is very popular among Mahayana Buddhists both for its brevity and depth of meaning. Heart of Wisdom contains a translation of the Sutra as well as a word by word commentary. Emptiness is not easy to understand but as the author explains: David Vennells supports this observation: Heart of Wisdom explains the philosophical implications of emptiness in practical, everyday terms for both the scholar and the lay reader. In his book Reiki Mastery, David Vennells says: