And he said unto them, Unto you it is given to know the mystery of the kingdom of God: but unto them that are without, all these things are done in parables: That seeing they may see, and not perceive; and hearing they may hear, and not understand; lest at any time they should be converted, and their sins should be forgiven them." -- Mark 4:10-12 "And when he (Jesus) was alone, they that were about him with the twelve asked of him the parable.
So here we have Jesus telling us He speaks in parables so that those who have been given ears to hear will hear and understand, and those who "are without" will not understand and be saved.
See? Is that so difficult to understand? (And it's not even said in a parable.)
Not unless you try to make TULIPs out of it.