To what shall I compare the kingdom of God?
It is like unto a leukemia patient's course of treatment. First they use radiation to kill the diseased bone-marrow. Then they replace it with a bone-marrow transplant.
Let him hear who has ears to distinguish between Law and Gospel.
FOOTNOTE: This parable could also be used to answer those who say, "You shouldn't point out false teachings. Just say what you have to say, and let the other guys say what they have to say, and it will straighten itself out..."