Then Peter said to Jesus, "Explain to us the parable that says people aren't defiled by what they eat."
"Don't you understand yet?" Jesus asked. "Anything you eat passes through the stomach and then goes into the sewer. But the words you speak come from the heart — that's what defiles you. For from the heart come evil thoughts, murder, adultery, all sexual immorality, theft, lying, and slander. These are what defile you. Eating with unwashed hands will never defile you."
— Matthew 15:15-20 NLT
Jesus had to remind his disciples of this truth repeatedly: It's what's inside our hearts that leads to what we say and do. Of course, it's possible that we can think something nice, feel something nice, but then let those feelings and thoughts take the place of actions. Fortunately, it's also possible not to act on bad feelings and thoughts. On the other hand, when we do something, it's the interior world of the heart that leads to those actions. It's precisely because this interior world reveals itself in our behavior that we must keep our hearts pure.
Jesus is after right actions, good deeds, decent behavior, and honorable character. But these things are ultimately and consistently producible only if we keep our hearts pure and are committed to honor God in the way we live.
O Lord God, Almighty Creator and Sustainer, why you choose to love me and bless me with your grace is a great mystery to me. You know my thoughts. You know my motives. While I am working on making those areas of my life more holy, I recognize that I need the cleansing and power of your Holy Spirit in the inner most places of my existence. Cleanse my heart and conform my thoughts to your will. In Jesus' name, I pray. Amen.