Book excerpt: In his previous book, The Attention Revolution, bestselling author Alan Wallace guided readers through the stages of shamatha, a meditation for focusing the mind. In Stilling the Mind, he uses the wisdom of Dzogchen--the highest of all the meditation traditions--to open up the shamatha practice into a space of vast freedom. Here, Wallace introduces us to Dudjom Lingpa's Vajra Essence, one of the most cherished works of the Nyingma school from which Dzogchen stems. With his trademark enthusiasm and keen intelligence, Wallace makes obscure concepts intelligible to contemporary readers and allows us to glimpse the profound realizations of a great nineteenth-century spiritual adept.