The Sufis capture this idea [of how to stand guard over the gate of the mouth] in a splendid metaphor. They advise us to speak only after our words have managed to issue through three gates.
At the first gate we ask ourselves, “Are these words true?” If so, let them pass on; if not, back they go.
At the second gate, we ask, “Are they necessary?” They [our words] may be true, but it doesn’t follow that they have to be uttered; they must serve some meaningful purpose. Do they clarify the situation or help someone? Or do they strike a discordant or irrelevant note?
At the last gate we ask, “Are they kind?” If we still feel we must speak out, we need to choose words that will be supportive and loving, not words that embarrass or wound another person. All of us understand what blows can do to someone, but we do not realize that words can create a more painful injury, one that can last for many years. Nor do we understand the terribly destructive impact words can have on the consciousness of the person who uses them.— Eknath Easwaran in Meditation