Proverbs 15:4

Note, 1. A good tongue is healing, healing to wounded consciences by comforting them, to sin-sick souls by convincing them, to peace and love when it is broken by accommodating differences, compromising matters in variance, and reconciling parties at variance; this is the healing of the tongue, which is a tree of life, the leaves of which have a sanative virtue, Rev 22:2. He that knows how to discourse will make the place he lives in a paradise. 2. An evil tongue is wounding (perverseness, passion, falsehood, and filthiness there, are a breach in the spirit); it wounds the conscience of the evil speaker, and occasions either guilt or grief to the hearers, and both are to be reckoned breaches in the spirit. Hard words indeed break no bones, but many a heart has been broken by them.

— Matthew Henry's Concise Commentary (public domain)

A wholesome tongue--(Compare Margin), pacifying and soothing language. tree of life-- (Pro 3:18; Pro 11:30). perverseness therein--cross, ill-natured language. breach . . . spirit--(compare Isa 65:14, Hebrew), grieves, instead of appeasing.

— Jamieson-Fausset-Brown Commentary (public domain)