The Imitation of Christ, by Thomas a Kempis, tr. by William Benham [1886], at sacred-texts.com
We cannot place too little confidence in ourselves, because grace and understanding are often lacking to us. Little light is there within us, and what we have we quickly lose by negligence. Oftentimes we perceive not how great is our inward blindness. We often do ill and excuse it worse. Sometimes we are moved by passion and count it zeal; we blame little faults in others and pass over great faults in ourselves. Quickly enough we feel and reckon up what we bear at the hands of others, but we reflect not how much others are bearing from us. He who would weigh well and rightly his own doings would not be the man to judge severely of another.
2. The spiritually-minded man putteth care of himself before all cares; and he who diligently attendeth to himself easily keepeth silence concerning others. Thou wilt never be spiritually minded and godly unless thou art silent concerning other men's matters and take full heed to thyself. If thou think wholly upon thyself and upon God, what thou seest out of doors shall move thee little. Where art thou when thou art not present to thyself? and when thou hast overrun all things, what hath it profited thee, thyself being neglected? If thou wouldst have peace and true unity, thou must put aside all other things, and gaze only upon thyself.
3. Then thou shalt make great progress if thou keep thyself free from all temporal care. Thou shalt lamentably fall away if thou set a value upon any worldly thing. Let nothing be great, nothing high, nothing pleasing, nothing acceptable unto thee, save God Himself or the things of God. Reckon as altogether vain whatsoever consolation comes to thee from a creature. The soul that loveth God looketh not to anything that is beneath God. God alone is eternal and incomprehensible, filling all things, the solace of the soul, and the true joy of the heart.