653. Everyone knows that a lamb cannot act except like a lamb, nor a sheep except like a sheep. On the other hand a wolf cannot act except like a wolf, nor a tiger except like a tiger. If those animals were mixed together, would not the wolf devour the lamb and the tiger the sheep? That is why shepherds are set to guard them. Everyone knows that a spring of sweet water cannot produce bitter water from its stream; and that a good tree cannot produce bad fruit. A vine cannot prick like a thorn, the flower of the lily cannot scratch like a briar, or the hyacinth claw like the thistle; nor can the thorn, briar or thistle behave like the vine, lily or hyacinth. These weeds are therefore rooted out of fields, vineyards and gardens, gathered into heaps and thrown on a fire. Much the same happens to the wicked who arrive in the spiritual world, as the Lord's words say (Matthew 13:30; John 15:6). The Lord also said to the Jews:

You brood of vipers, how can you speak good when you are wicked? The good man puts forth good things from the good treasury of his heart, and the wicked man puts forth evil from his wicked treasury, Matthew 12:34-35.