The Imitation of Christ, by Thomas a Kempis, tr. by William Benham , at sacred-texts.com
Thou oughtest to seek earnestly the grace of devotion, to ask it fervently, to wait for it patiently and faithfully, to receive it gratefully, to preserve it humbly, to work with it diligently, and to leave to God the time and manner of heavenly visitation until it come. Chiefly oughtest thou to humble thyself when thou feelest inwardly little or no devotion, yet not to be too much cast down, nor to grieve out of measure. God ofttimes giveth in one short moment what He hath long time denied; He sometimes giveth at the end what at the beginning of prayer He hath deferred to give.
2. If grace were always given immediately, and were at hand at the wish, it would be hardly bearable to weak man. Wherefore the grace of devotion is to be waited for with a good hope and with humble patience. Yet impute it to thyself and to thy sins when it is not given, or when it is mysteriously taken away. It is sometimes a small thing which hindereth and hideth grace; (if indeed that ought to be called small and not rather great, which hindereth so great a good); but if thou remove this, be it small or great, and perfectly overcome it, thou wilt have what thou hast asked.
3. For immediately that thou hast given thyself unto God with all thine heart, and hast sought neither this nor that according to thine own will and pleasure, but hast altogether settled thyself in Him, thou shalt find thyself united and at peace; because nothing shall give thee so sweet relish and delight, as the good pleasure of the Divine will. Whosoever therefore shall have lifted up his will unto God with singleness of heart, and shall have delivered himself from every inordinate love or dislike of any created thing, he will be the most fit for receiving grace, and worthy of the gift of devotion. For where the Lord findeth empty vessels,(1) there giveth He His blessing. And the more perfectly a man forsaketh things which cannot profit, and the more he dieth to himself, the more quickly doth grace come, the more plentifully doth it enter in, and the higher doth it lift up the free heart.
4. Then shall he see, and flow together, and wonder, and his heart shall be enlarged within him,(2) because the hand of the Lord is with him, and he hath put himself wholly in His hand, even for ever. Lo, thus shall the man be blessed, that seeketh God with all his heart, and receiveth not his soul in vain. This man in receiving the Holy Eucharist obtaineth the great grace of Divine Union; because he hath not regard to his own devotion and comfort, but, above all devotion and comfort, to the glory and honour of God.
(1) 2 Kings iv. (2) Isaiah lx. 5.