What does Psalm 41:6 mean?

The inspiration for this psalm was most likely the rebellion led by David's son, Absalom, and David's trusted advisor, Ahithophel (2 Samuel 15—18). Not only would David have to contend with open enemies, but he'd also need to watch for false friends. In this verse, he notes that some who pretend to be helpful are insincere: their words are "empty." Worse, when they leave, they maliciously spread rumors and gossip. This parallels the experience of Job; his story reminds us that some so-called-comforters are no comfort at all (Job 42:7).

Proverbs 6:16–19 records a series of sins which God especially detests. David's hypocritical visitors displayed at least four of those things: "a lying tongue," "a heart that devises wicked plans," "feet that make haste to run to evil," and "a false witness who breathes out lies." The apostle Peter urges Christians to "put away all malice and all deceit and hypocrisy and envy and all slander" (1 Peter 2:1). Instead of retaining such evil traits, Christians ought to "long for the pure spiritual milk, that by it [they] may grow up into salvation" (1 Peter 2:2).