1 Kings 10:1-10; Psalm 36(37):5-6,30-31,39-40; Mark 7:14-23
"Its what comes out of a person that makes them unclean" . .
Take this parable just as it is written, and you find a slightly humorous (if maybe in a slightly tasteless way?) argument that what you eat is irrelevant as it all ends up in the sewer anyhow. There is even an aside ('thus he pronounced all foods as clean") to help us see that.
But are parables meant to have deeper, hidden meanings?
Often - usually indeed. In this case - is it a way of commenting on the scribes and pharisees? Jesus might be saying that what comes out (of their mouths) is unclean. They would have been teaching a commitment to Mosaic tradition and law - which very strictly govern what may (and may not) be eaten. We too, can burden ourselves and others with regulation and scrupulosity. It is the over zealous attention to rules that can lead us away from God - we become focused on doing the right things, and not enough attention being paid to why.
We can protect ourselves from this by sticking to just what is important. Love God, and Love your neighbour. Aim for those and not much can go wrong!