It seems fitting to begin with a tribute to the late Henry Chadwick, whose thorough, even-handed, and ever readable work contributed much to our understanding of the theme of sanctity in the early Church. In particular, his address at a conference on ‘The Byzantine Saint’ held in Birmingham in 1980 exemplified his capacity to identify and constructively pursue the broad issues at stake. In speaking of the early saints and the content of their lives, Chadwick explains, ‘we are tempted either to tell the stories of their mortifications and then, as was said of Lytton Strachey, ostentatiously refrain from laughing, or we go in search of trendy non-religious explanations of the social needs that created them’. He goes on to acknowledge, as most would, the importance of sociological interpretations and their potential for the study of sanctity, but warns that ‘a stripping away of their religious motivation will leave the historian with a distorted picture’. It is along this route of keeping the religious or theological motivations and presuppositions of sanctity in mind, that the present essay will proceed. It focuses on the neglected concept of μετάνoια or ‘repentance’ (lit. a ‘change of mind’) which dominates much of the ascetic theology of the early Christian East, particularly as expounded by the influential fifth-century theologian Mark the Monk (or ‘the Hermit’ / ‘the Ascetic’).