The Mystagogy of St Maximos

   This, indeed is why the blessed old man believed that every Christian should be exhorted--and he never failed to do this---to frequent God's holy church and never to abandon the holy synaxis accomplished therein because of the holy angels who remain there  and who take note each time people who enter and present themselves to God, and they make supplications for them; likewise because of the grace of the Holy Spirit which is always invisibly present, but in a special way at the time of the holy synaxis. This grace transforms and changes each person who is found there and in fact remolds him in proportion to what is more divine in him and  leads him to what is revealed through the mysteries which are celebrated, even if he does not himself feel this because he is still among those who are children in Christ, unable to see either into the depths of the reality or the grace operating in it, which is revealed through each of the divine symbols of salvation being accomplished , and which proceeds according to the order and progression from preliminaries  to the end of everything.

from Chapter 24

St Maximos the Confessor, Century on Various Texts

A pure heart is one which offers the mind to God free of all image and form, and ready to be imprinted only with his own archetypes, by which God Himself is made manifest.

Text 82

From St Dionysios' Mystical Theology

We therefore maintain that the universal and transcendent Cause of all things is neither without being nor without life, nor without reason or intelligence; nor is it a body, nor has it form or shape, quality, quantity or weight; nor has it any localized, visible or tangible existence; it is not sensible or perceptible; nor is it subject to any disorder or inordination nor influenced by any earthly passion; neither is it rendered impotent through the effects of material causes and events; it needs no light; it suffers no change, corruption, division, privation or flux; none of these things can either be identified with or attributed unto it.