I find it personally interesting that Luther was attracted to mysticism, but unable to make much of it.
Martin also pursued his lifelong unhappy love, mysticism.
All the primitive superstition and German simplicity in him should have found refuge in the mystic’s unification with God which needed no formula of justification and which, in fact, left all “thinking” aside. He did yearn for the birth of God’s “uncreated word” in his soul; he desired to be physically pervaded with the kind of assurance “that really gets under your skin” (senkt sich ins Fleisch). The mystic proclaims as attainable exactly that total piety which Martin desired (tota corde and tola mente; omni affectu and toto intellects). Bonaventura “drove him nearly mad” with his advice that it is better to turn to grace than to dogma; to nostalgia than to intellect; and to prayer than to study. But, alas, Martin had to admit that he never “tasted” the fruits of such endeavor (ullum unquam gustum . . . sensi) sincerely as he had tried. He could not feel his way to God.
Erik Erikson, Young Man Luther, p.164