And then he added, “It is what comes from inside that defiles you. For from within, out of a person’s heart, come evil thoughts, sexual immorality, theft, murder, adultery, greed, wickedness, deceit, lustful desires, envy, slander, pride, and foolishness. All these vile things come from within; they are what defile you.”
In this section of scripture, Jesus had just finished a discourse with a group of Pharisees and scribes. They had come from Jerusalem, most likely at the request of a Galilean Pharisee. They were hoping to trap Jesus in a discussion surrounding the laws and customs of Judaism. However, in the end they were unable to do so and instead Jesus rebuked them because their hearts were not toward God. Instead of honoring God with their laws and customs, the Pharisees used their laws and customs to actually disobey God, they did so in order to gain profit and public recognition for themselves. Once in private, the disciples who were confused over the parable spoken by Jesus asked Him the meaning of the parable, which Jesus explains in this section of scripture. We need to keep in mind the disciples were raised in Judaism.
They were raised under the Pharisaical system which relied on salvation by works. So they grew up in a system where your social piety was based on your external religious acts and not on where your heart was toward God. And what Jesus explains is that following God is a matter of the heart and not a matter of customs and rituals. What defiles us is the intentions and thoughts of our heart. And it is from the desires of our heart that evil behavior is born. Which means either we have a heart toward God through faith or we don’t! There is no system of works or rituals we can perform through which we can earn our salvation. To sum it up, it’s our faith in Jesus not our good deeds that determines our salvation. God looks at our hearts, He is interested in those who have a heart toward Him and a love for His word. The Old Testament laws were meant to show us our need for a Savior. They were meant to show us that no matter what, no one could be justified by the law.