Cain killing Abel, Hans Acker, c. 1430, Ulm Münster Cathedral
For this is the message which you have heard from the beginning, that we should love one another, and not be like Cain who was of the evil one and murdered his brother. And why did he murder him? Because his own deeds were evil and his brother’s righteous. 1 John 3:11-12
Abel’s sacrifice was acceptable to God, Cain’s was not. It was the interior disposition of Cain’s heart toward his brother that led him to sin. It was the sin of envy that festered in Cain’s heart, leading to anger, and ultimately the murder of his brother.
St. Thomas Aquinas defines envy as sorrow for another’s good. Envy is not the greatest sin but “it is the only one that gives the sinner no pleasure at all,” says Peter Kreeft in his book Back to Virtue. “It causes nothing but pain and sorrow. Thus it shows more clearly than other sins two profound truths about the nature of sin: that it removes our joy and that it is deceptive,” he adds. “Envy removes joy because envy is the opposite of gratitude, and gratitude is the seedbed of joy.”