Desires are kindled in us in two ways: by the cry of prayer, which makes one groan with the murmuring of one's heart, and by a flash of apprehension by which the mind turns most directly and intensely to the rays of light [Ps., 37, 9].
Therefore to the cry of prayer through Christ crucified, by Whose blood we are purged of the filth of vice, do I first invite the reader, lest perchance he should believe that it suffices to read without unction, speculate without devotion, investigate without wonder, examine without exultation, work without piety, know without love, understand without humility, be zealous without divine grace, see without wisdom divinely inspired. Therefore to those predisposed by divine grace, to the humble and the pious, to those filled with compunction and devotion, anointed with the oil of gladness [Ps., 44, 8], to the lovers of divine wisdom, inflamed with desire for it, to those wishing to give themselves over to praising God, to wondering over Him and to delighting in Him, do I propose the following reflections, hinting that little or nothing is the outer mirror unless the mirror of the mind be clear and polished.
Bestir yourself then, O man of God, you who previously resisted the pricks of conscience, before you raise your eyes to the rays of wisdom shining in that mirror, lest by chance you fall into the lower pit of shadows from the contemplation of those rays.
St. Bonaventure, Journey of the Mind into God, Prologue.