Proverbs 12:18 uses the word "piercings" — the wounds of a sword. This is not a metaphor for mild unkindness. James 3:9 adds the theological dimension: to curse a person made in God's image is to attack the image of God himself. The person being verbally abused is the image-bearer; the damage to them has a theological character.
Ephesians 4:29 defines speech by what it produces in the listener: it should "minister grace." This is not merely a standard for what not to say — it is a positive description of what words are for. Speech that tears down, demeans, or systematically distorts another person's sense of reality is the precise opposite of what Ephesians describes. God's design for language was not neutral; it was constructive.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.