This extensive treatise on the prayer of the heart ranges over a broad field of topics on how to acquire pure prayer including the methods of fasting, the importance of the Holy Mysteries, the nature of faith, the arrangement of the day, the signposts of progress in prayer, the dangers of prelest, the nature of repentance, and the acquisition of passionlessness. In this treatise the authors make a cogent argument for the frequent reception of Holy Communion. This lengthy and thorough treatise is arranged in the genre of the Century, and authored by the great 14th century Saint-Patriarch of Constantinople Kallistos I and his co-laborer, St. Ignatios of Xanthopoulos. St. Kallistos was a spiritual son of St. Gregory of Sinai (also an author in the Philokalia) for many years on Mt. Athos.