Chapter 28 — Part III: The Decalogue — The Fifth Commandment
Section 35. Moreover, there are many evil consequences and sins which are linked together with this one sin of hatred. Hence these words of St. John: He that hateth his brother, is in darkness, and walketh in darkness, and knoweth not whither he goeth; because the darkness hath blinded his eyes. He must, therefore, frequently fall; for how can anyone view in a favourable light the words or actions of him whom he hates? Hence arise rash and unjust judgments, anger, envy, detractions, and other evils of the same sort, in which are often involved those who are connected by ties of friendship or blood; and thus does it frequently happen that this one sin is the prolific source of many.