It's almost glaring, the way the Gospel for today seems to outright contradict the first reading. Mark depicts Jesus teaching about the Kosher laws and declaring all foods clean, "incapable of defiling a person." But in the Garden of Eden, God definitely warned "the man" that if he ate from "the tree of knowledge of good and evil," not only would he be defiled, he would DIE.
Pretty drastic difference.
And yet it's not that different after all. If you read the whole of today's Gospel passage, you would find a whole ugly list: evil thoughts, unchastity, theft, murder, adultery, greed, malice... All forms of the "knowledge of evil." Because in the Bible, knowledge is never something abstract. You only know something if you experience it.
Sad to say, we all know what happens next in the story. All those evils Jesus listed with such distaste came to live in the human heart, and they've been pouring back out ever since. It almost makes us want to blame God for putting the tree there in the first place.
But there had to be a tree of "knowlege of good and evil" in the Garden, because God made man free. Not free for evil, but free for good. And the only way he could "know" that good was by choosing to make it part of himself. Eating it, as it were.
Recommended: Simone Weil's remarkable, if eccentric, essays on eating in (I think)
Waiting for God