Proverbs 15:4 A wholesome tongue is a tree of life: but perverseness therein is a breach in the spirit.
This promise is not worded like a promise, but it has the same effect as all the conditional promises regarding the tongue. If you speak wholesome words in wholesome way, then you will cause life to flourish in both the speaker and the hearer. As usual, our words and how we speak them will tend either toward life or toward death. That sounds serious, and it is. We will give account for every idle word, and the effects of our tongues is a life or death matter. It may not feel to us like it matters that much what we say or how we say it, but since God says the tongue has great power in its effects then it does.
This promise and its negative warning is an incentive and an encouragement for us to watch what we say and how we say it. Remember that the Lord has given us the promise and the power to enhance life and its joy in ourselves and others. The tongue has the power to make people feel better.
In place of a “wholesome” tongue other translations use “gentle” or “healing” tongue. Gentle words spoken in a healing or soothing way are a tree of life. Just like the Tree of Life such words have an eternal effect in forever reward and blessing.
Conversely, a perverse tongue brings in death. It causes “a breach in the spirit,” allowing Satan and Evil to enter the soul and gain a foothold. But regular repentance and forgiveness through the gospel closes up the breach and gives life. “Let no unwholesome word proceed out of your mouth, but only that which gives a blessing.” There is a promise attached.