There is nothing from without a man, that entering into him can defile him: but the things which come out of him, those are they that defile the man. If any man have ears to hear, let him hear. And when he was entered into the house from the people, his disciples asked him concerning the parable. Mark 7:15-17

Jesus made the statement “You are defiled by what’s within You” The Religious leaders were very careful to make sure they didn’t defile themselves from the outside by washing their hands, staying away from outsiders or lepers, ect, However Jesus is talking about a heart issue, not a cleanliness issue. 

As Jesus taught in Matthew 5 “Anyone who has already lusted after a woman has committed adultery in their heart” (Matthew 5:28) or “Anyone who hates his brother has already committed murder in their hearts “ (Matthew 5:22) Sin is a heart issue, its not a ritual issue. This is why Jesus stated we defile ourselves from within, Sin begins in our hearts. This is why we need to become Born Again, and have a clean heart and mind

And he saith unto them, Are ye so without understanding also? Do ye not perceive, that whatsoever thing from without entereth into the man, it cannot defile him; Because it entereth not into his heart, but into the belly, and goeth out into the draught, purging all meats? And he said, That which cometh out of the man, that defileth the man. Mark 7:18-20

The disciples didn’t understand what Jesus was teaching them, remember they were raised in the Mosaic Law, therefore their mindsets were focused on the food laws and the customs. However Jesus is demonstrating the New Covenant here, by declaring that all foods are clean. Who else could do this but God alone?

For from within, out of the heart of men, proceed evil thoughts, adulteries, fornications, murders, Thefts, covetousness, wickedness, deceit, lasciviousness, an evil eye, blasphemy, pride, foolishness: All these evil things come from within, and defile the man. Mark 7:21-23

Jesus revealed to his disciples what he was talking about, its the evil from within that defiles us. Our thoughts, lust, blasphemy, pride, ect. These things contaminate  our hearts and make us perform evil deeds, this again is why we need to become Born Again (John 3)

The religious leaders thought they were righteous based on their outside works, but as Jesus stated they were “Whitewashed Tombs”, nice looking on the outside but dead on the inside, why? Because their hearts and minds were filled with evilness, they were defiled from within!