The weeping and gnashing of teeth refer to the greatest possible suffering, conveyed in the Greek word klauthmos, which is the sadness felt when suffering a loss (Matthew 2:18, Acts 20:37). Those in the darkness gnash their teeth in powerless fury and despair, because their suffering will never end (see Daniel 12:2; Matthew 3:12, Matthew 18:8, Matthew 25:46)—primarily a spiritual, rather than a physical, anguish.
The weeping and gnashing of teeth serves to indicate the greatest conceivable form of suffering. The Greek word klauthmos expresses that sadness experienced when suffering a loss (Matthew 2:18; Acts 20:37). The gnashing of teeth indicates powerlessness and despair combined with fury and anger. The prospect these people face is, after all, a never-ending suffering (see Daniel 12:2, Matthew 3:12, Matthew 18:8, Matthew 25:46).1
Weeping is an expression of their sadness, while the gnashing of teeth points to perpetual suffering. These expressions indicate the pain of hell, which is first and foremost a spiritual as opposed to a physical form of suffering.2
11 I tell you, many will come from east and west and recline at table with Abraham, Isaac, and Jacob in the kingdom of heaven,