"A good man out of the good treasure of his heart brings forth good; and an evil man out of the evil treasure of his heart brings forth evil. For out of the abundance of the heart his mouth speaks." (Luke 6:45)
We've all been around people who are cynical and negative. I don't know about you, but a little of that goes a long way. I've had co-workers, friends and relatives who, because of that particular trait, I could only do in short doses. That kind of conversation tears at our souls and brings us down. It readily leads to sin as it frequently involves gossip and hard judgments against others.
Hebrews 4:12 tells us that "the Word of God is living and powerful, and sharper than any two-edged sword, piercing even to the division of soul and spirit, and of joints and marrow, and is a discerner of the thoughts and intents of the heart." The Bible has much to say about our mouths and how they ought to be used, but in Luke 6 Jesus brings it all into sharp focus by targeting the real culprit -- our hearts. The original word for heart in Luke 6:45 and Hebrews 4:12 is the Greek word kardia. In this context it refers to the soul. The soul is the seat of our mind, will, and emotions.
People are sometimes good fakers, but given enough time hearts are exposed. I've met folks, who at the start, seemed to be really great people, but as time went on their heart issues began to show. People can fake it in the short term, but given enough time what is really in their hearts will come out. The abundance of their heart, or lack thereof, will be revealed. You really can't maintain what you don't have to give out. This is actually a good thing because it reveals needs and wounds and can open up real opportunities for healing and growth.
I love the statement in Hebrews 4:12 that the Word of God is "a discerner of the thoughts and intents of the heart." The Word of God is like a mirror we can hold our lives up against to see how we line up. Maybe I have been holding onto unforgiveness against someone and in reading the Bible I discover that Jesus commanded us to forgive (Mark 11:25). At that point my heart has been revealed and I have a choice -- I can either continue to do things my way or submit to what the Lord has said.
The car and feeding of our souls is critically important. If you desire an abundant heart it matters what you are reading, watching, talking about and thinking on. God's Word is vitally important in this process. Reading and meditating on it and applying it to your life will transform you. Of course, that has to take place in the context of our relationship and fellowship with the Lord or we can turn it into dry religion, in which case, it will avail us little.