Thomas a Kempis, The Imitation of Christ 1.14

On avoiding rash judgment

1. Look well unto yourself, and beware that you judge not the doings of others. In judging others a man labors in vain; he often errs, and easily falls into sin; but in judging and examining himself he always labors to good purpose. According as a matter touches our fancy, so oftentimes do we judge of it; for easily do we fail of true judgment because of our own personal feeling. If God were always the sole object of our desire, we should the less easily be troubled by the erring judgment of our fancy.

2. But often some secret thought lurking within us, or even some outward circumstance, turns us aside. Many are secretly seeking their own ends in what they do, yet know it not. They seem to live in good peace of mind so long as things go well with them, and according to their desires, but if their desires are frustrated and broken, immediately they are shaken and displeased. Diversity of feelings and opinions very often brings about dissensions between friends, between countrymen, between religious and godly men.

3. Established custom is not easily relinquished, and no man is very easily led to see with the eyes of another. If you rest more upon your own reason or experience than upon the power of Jesus Christ, your light shall come slowly and hardly; for God wills us to be perfectly subject unto Himself, and all our reason to be exalted by abundant love towards Him.