The teaching of St Gregory is so fundamental to Orthodoxy that he is especially commemorated each year in Great Lent on the Sunday following the Sunday of Orthodoxy (as well as on Nov. 14); Bishop Kallistos observes in the English edition of the Philokalia, "his successful defence of the divine and uncreated character of the light of Tabor...[is] seen as a direct continuation of the preceding celebration, as nothing less than a renewed Triumph of Orthodoxy."
The son of a prominent family, St Gregory was born (1296) and raised in Constantinople. At about age twenty, he abandoned a promising secular career to become a monk on Mt Athos. (His family joined him en masse: two of his brothers went with him to the Holy Mountain; at the same time his widowed mother, two of his sisters, and many of the household servants also entered monastic life.) He spent the next twenty years living as a hermit, spending five days a week in complete solitude, then joining the brethren on weekends for the