The late Middle Ages have often been described as a time of general moral and ethical decline, and especially as a time of anti-clericalism, hence also of widespread secularization, which ultimately led, as a counter-reaction, to the Protestant Reformation in 1517. In reality, however, there were many religious reform movements underway already since the late fourteenth century, most famously the Devotio moderna, initiated and deeply influenced by Jan van Ruysbroeck (1293-1381), Geert Groote (1340-1384) and Thomas a Kempis, who all aimed for a new form of spiritual, individualized piety, closely related to, but not to be confused with, medieval mysticism. They insisted on a simple life style (simplicitas Christianismi) …
Classen, Albrecht. "Thomas à Kempis". The Literary Encyclopedia. First published 18 January 2005; last revised 30 November -1.
[http://www.litencyc.com/php/speople.php?rec=true&UID=2, accessed 27 April 2015.]