Mysticism, always present within the Church from Paul himself, grew stronger in the fourteenth and fifteenth centuries as a natural reaction to the rationalism of the scholastics and the increasing mechanical formalism of the ecclesiastical system. The great German mystics, Master Eckhart, Tauler, Suso, and the author of the Theologia Germanica that so powerfully influenced Luther, emphasized personal salvation to the exclusion of everything else. This they sought to effect by a direct union  with the Divine Being, which was brought about by meditation and prayer without the intermediary of any priest or sacrament. While they did not deny the traditional doctrines, they relegated them to the background as unimportant, and hence proved a disintegrating force. In the words of the Theologia Germanica, “Now mark what may help or further us towards union with God. Behold, neither exercises, nor words, nor works, nor any creature, nor creature’s work, can do this. In this wise, therefore, must we renounce and forsake all things, that we must not imagine or suppose that any words, works, or exercises, any skill, or cunning, or any created thing can help or serve us thereto. Therefore we must suffer these things to be what they are, and enter into the union with God.” In the fourteenth century a simple and devout piety of this sort was widespread in Germany.
— John Herman Randall, The Making of the Modern Mind: a survey of the intellectual background of the present age (Cambridge, MA: Houghton Mifflin Co., 1940), pp. 145-46.