Thomas a Kempis, The Imitation of Christ 1.7

Of fleeing from vain hope and pride

1. Vain is the life of that man who puts his trust in men or in any created Thing. Be not ashamed to be the servant of others for the love of Jesus Christ, and to be reckoned poor in this life. Rest not upon yourself, but build your hope in God. Do what lies in your power, and God will help your good intent. Trust not in your learning, nor in the cleverness of any that lives, but rather trust in the favor of God, who resists the proud and gives grace to the humble.

2. Boast not of yourself in your riches if you have them, nor in your friends if they are powerful, but in God, who gives all things, and in addition to all things desires to give even Himself. Be not lifted up because of your strength or beauty of body, for with only a slight sickness it will fail and wither away. Be not vain of your skilfulness or ability, lest you displease God, from whom comes every good gift that we have.

3. Count not yourself better than others, lest perchance you appear worse in the sight of God, who knows what is in man. Be not proud of your good works, for God's judgments are of another sort than the judgments of man, and what pleases man is often displeasing to Him. If you have any good, believe that others have more, and so you may preserve your humility. It is no harm to you if you place yourself below all others; but it is great harm if you place yourself above even one. Peace is ever with the humble man, but in the heart of the proud there is envy and continual wrath.