The Imitation of Christ, by Thomas a Kempis, tr. by William Benham , at sacred-texts.com
Thou must take heed of curious and useless searching into this most profound Sacrament, if thou wilt not be plunged into the abyss of doubt. He that is a searcher of Majesty shall be oppressed by the glory thereof.(1) God is able to do more than man can understand. A pious and humble search after truth is to be allowed, when it is always ready to be taught, and striving to walk after the wholesome opinions of the fathers.
2. Blessed is the simplicity which leaveth alone the difficult paths of questionings, and followeth the plain and firm steps of God's commandments. Many have lost devotion whilst they sought to search into deeper things. Faith is required of thee, and a sincere life, not loftiness of intellect, nor deepness in the mysteries of God. If thou understandest not nor comprehendest the things which are beneath thee, how shalt thou comprehend those which are above thee? Submit thyself unto God, and humble thy sense to faith, and the light of knowledge shall be given thee, as shall be profitable and necessary unto thee.
3. There are some who are grievously tempted concerning faith and the Sacrament; but this is not to be imputed to themselves but rather to the enemy. Care not then for this, dispute not with thine own thoughts, nor make answer to the doubts which are cast into thee by the devil; but believe the words of God, believe His Saints and Prophets, and the wicked enemy shall flee from thee. Often it profiteth much, that the servant of God endureth such things. For the enemy tempteth not unbelievers and sinners, because he already hath secure possession of them; but he tempteth and harasseth the faithful and devout by various means.
4. Go forward therefore with simple and undoubting faith, and draw nigh unto the Sacrament with supplicating reverence. And whatsoever thou art not enabled to understand, that commit without anxiety to Almighty God. God deceiveth thee not; he is deceived who believeth too much in himself. God walketh with the simple, revealeth Himself to the humble, giveth understanding to babes, openeth the sense to pure minds, and hideth grace from the curious and proud. Human reason is weak and may be deceived; but true faith cannot be deceived.
5. All reason and natural investigation ought to follow faith, not to precede, nor to break it. For faith and love do here especially take the highest place, and work in hidden ways in this most holy and exceeding excellent Sacrament. God who is eternal and incomprehensible, and of infinite power, doth great and inscrutable things in heaven and in earth, and His wonderful works are past finding out. If the works of God were of such sort that they might easily be comprehended by human reason, they should no longer be called wonderful or unspeakable.
(1) Proverbs xxv. 27 (Vulg.)