Thomas a Kempis, The Imitation of Christ 2.5

Of self-esteem

1. 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 puts care of himself before all cares; and he who diligently attends to himself easily keeps silence concerning others.You will never be spiritually minded and godly unless you are silent concerning other men's matters and take full heed of yourself. If you think wholly upon yourself and upon God, what you see out of doors shall move you little. Where are you when you are not present to yourself? And when you have overrun all things, what has it profited you, yourself being neglected? If you would have peace and true unity, you must put aside all other things, and gaze only upon yourself.

3. Then you shall make great progress if you keep yourself free from all temporal care.You shall lamentably fall away if you set a value upon any worldly thing. Let nothing be great, nothing high, nothing pleasing, nothing acceptable unto you, save God Himself or the things of God. Reckon as altogether vain whatsoever consolation comes to you from a creature. The soul that loves God looks 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.