Mark‬ ‭7:18-23 NIV‬‬
“Are you so dull?” he asked. “Don’t you see that nothing that enters a person from the outside can defile them? For it doesn’t go into their heart but into their stomach, and then out of the body.” (In saying this, Jesus declared all foods clean.) He went on: “What comes out of a person is what defiles them. For it is from within, out of a person’s heart, that evil thoughts come—sexual immorality, theft, murder, adultery, greed, malice, deceit, lewdness, envy, slander, arrogance and folly. All these evils come from inside and defile a person.”

In the teaching of Jesus above, we learn that what we let into our heart can cause us to sin. That’s why we should be very careful about what we allow into our heart since it is going to show up in our lives. You see, before all of those sins Jesus mentioned came out in a person’s actions, they first started as a thought in his or her heart. The more we dwell/meditate upon something within ourselves, we are watering that seed and we will eventually see the fruit in our lives, whether it is good or bad. This is why if something evil comes into our heart, we should repent and discard it right away by changing our attention to Jesus and what His Word says.

What we should sow into our hearts are the fruits of the Spirit such as love, joy, peace, kindness and self-control (Galatians 5:22-23). When the thoughts/meditations of our heart line up with those godly traits, we can be sure that our lives will be a reflection of Christ.

‭‭Proverbs‬ ‭4:23‬ ‭NIV
Above all else, guard your heart, for everything you do flows from it.