It is what comes out of a person that defiles them

Mark 7:1-23
You have a fine way of setting aside the commands of God in order to observe your own traditions!
Thus you nullify the word of God by your tradition that you have handed down. And you do many things like that.
Nothing outside a person can defile them by going into them. Rather, it is what comes out of a person that defiles them.
What comes out of a person is what defiles them. For it is from within, out of  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.
Mark adds an explanatory not for non-Jewish readers. The washing rituals had to do with religious 'cleanness', not simply hygiene or table manners. But it is possible for the observance of  'tradition' to empty God's plain command of all meaning. Jesus points out that humanity's real problem is not dirty hands but the deep-down pollution of washing can clean. The unclean food is as much part of Jewish thinking that even the disciples need further explanation.
Why?
Observe humans traditions sometime missed the real meaning of the commands of God.
Each church has their own tradition because of church are made by men. But be careful do not let tradition makes the truth missing.
Outside dirty can not defile others, but what comes out of a person that defiles others. Such as thoughts, sexual immorality, theft, murder, greed, malice...etc.
How?
Be careful keep our heart with clean mind and soul! Don't let tradition defile out heart!