Jesus reminds us that our speech and actions reveal the true underlying beliefs, attitudes, and motivations. The good impressions we try to make cannot last if our hearts are deceptive. What is in your heart will come out in your speech and behavior.
A good person produces good things from the treasury of a good heart, and an evil person produces evil things from the treasury of an evil heart. What you say flows from what is in your heart. (Luke 6:45 NLT)