The theme of speech is frequently visited in both the Psalms and Proverbs as this is the ultimate betrayal of one’s true spiritual condition:
“Do you not understand that everything that goes into the mouth passes into the stomach, and is eliminated? But the things that proceed out of the mouth come from the heart, and those defile the man. For out of the heart come evil thoughts, murders, adulteries, fornications, thefts, false witness, slanders. These are the things which defile the man; but to eat with unwashed hands does not defile the man.”
— Matthew 15:17-20
Here we are presented with the contrast of man’s words versus God’s words.