"Healing words give life, but dishonest words crush the spirit" (Prov. 15:4).
Dishonest words crush not only the spirit of another person, but also crush relationships - those between people, and those between a person and his or her God. Dishonesty is a poison. It makes for a toxic situation because fear, resentment and uncertainty are introduced into the relationship. Trust begins to wither, or even dies.
Intimacy cannot exist between two people when one or both refuse to be open and truthful with each other. Their relationship remains above ground; they are unable to send down strong roots to stabilize and grow their bond. The ground of their choices is too hard.
Dishonesty can be passive and silent also. Letting another think I believe something when I do not is deceptive. To entertain negative thoughts about or disagree with another's words or actions, then pretend the disagreement doesn't exist is deceptive also, is it not?
"You want me to be completely truthful, so teach me wisdom" (Psa 51:6).
"Do not lie to each other. You have left your old sinful life and the things you did before. You have begun to live the new life ... and are beginning to be like the One who made you" (Col 3:9, 10).