Mark 7: 14 - 23
14 And he called the people to him again, and said to them, "Hear me, all of you, and understand
15 there is nothing outside a man which by going into him can defile him; but the things which come out of a man are what defile him."
17 And when he had entered the house, and left the people, his disciples asked him about the parable.
18 And he said to them, "Then are you also without understanding? Do you not see that whatever goes into a man from outside cannot defile him,
19 since it enters, not his heart but his stomach, and so passes on?" (Thus he declared all foods clean.)
20 And he said, "What comes out of a man is what defiles a man.
21 For from within, out of the heart of man, come evil thoughts, fornication, theft, murder, adultery,
22 coveting, wickedness, deceit, licentiousness, envy, slander, pride, foolishness.
23 All these evil things come from within, and they defile a man."
---------------
Christ moves from the purification ritual straight to the dietary law. He is addressing the very identity of the Jewish faith. Jews throughout history chose death over violation of the dietary law. It is synonymous with the Jewish faith. The teaching is revolutionary, to a degree that we just plain can't understand today.
The teaching itself makes complete sense to anyone reading today. It is not goes in that's important, it's what comes out.
Look at the list of things that come out of the human heart. These are the ways of what Christ calls "the world", and Paul calls "the flesh." At least some of these things are active in every one of our lives, to some degree. You can't honestly look at yourself and not see these things.
We all have the stain of the world on us. We can at times be good and do our best to be moral, but it is only through Christ that we can convert from one to the other. That's our continuous call: repent from the world, and turn to the spirit.