Book excerpt: Maitreya's Ratnagotravibhaga, also known as the Uttaratantra, is the main Indian treatise on buddha nature, a concept that is heavily debated in Tibetan Buddhist philosophy. In A Direct Path to the Buddha Within, Klaus-Dieter Mathes looks at a pivotal Tibetan commentary on this text by Go Lotsawa Zhonu Pal, best known as the author of the Blue Annals. Go Lotsawa, whose teachers spanned the spectrum of Tibetan schools, developed a highly nuanced understanding of buddha nature, tying it in with mainstream Mahayana thought while avoiding contested aspects of the so-called empty-of-other (zhentong) approach. In addition to translating key portions of Go Lotsawa's commentary, Mathes provides an in-depth historical context, evaluating Go's position against those of other Kagyu, Nyingma, and Jonang masters and examining how Go Lotsawa's view affects his understanding of the buddha qualities, the concept of emptiness, and the practice of mahamudra.