What does Psalm 41:8 mean?

Upon leaving David, his hypocritical visitors told others his case was hopeless. "A deadly thing" may be translated, "a thing of Belial." The term Belial became a synonym for Satan, so it's possible David's foes connected his suffering with his sin (Psalm 41:4). Or, they may simply have seen his situation as hopelessly dire. While they spoke insincere words to David (Psalm 41:6), they plotted his doom and expected his imminent death (Psalm 41:7–8). During the rebellion of his son, Absalom (2 Samuel 15—18), David certainly faced extreme danger and political intrigue.

Wishing a person would die shows how wicked the human heart is. Jesus said, "For out of the heart come evil thoughts, murder, adultery, sexual immorality, theft, false witness, slander" (Matthews 15:19). Believers must never harbor evil thoughts toward another person. By contrast, they should "let love be genuine. Abhor what is evil; hold fast to what is good. Love one another with brotherly affection. Outdo one another in showing honor" (Romans 12:9–10).