"Out of the heart the mouth speaks," said Jesus, and a person's vocabulary is indeed a good indicator of who he or she truly is. Just as you can often tell where people are from by their accents, you may detect their internal culture through the content of their language. Complaining, swearing, gossip, cynicism, crudeness, etc. mark the speaker as a certain kind of person, while positive, self-controlled, uplifting, encouraging, and wholesome talk reveals a different sort of heart. Since the tongue is such a difficult thing to control (see James 3:7-8), it will sooner or later unmask us. What does your tongue say about your heart?
Out of the same mouth come praise and cursing.
My brothers, this should not be!
James 3:10