Why did Jesus use parables?

While Jesus was on the earth He spoke to the multitudes and Pharisees in parables often.  His disciples even asked this same question in Matthew 13:10. Jesus told them that He did so because it was fulfilling prophecy (Matthew 13:14).  Israel was to hear the message of God through the Messiah, but they were to not fully understand it.  While this sounds counterproductive, if it did not occur this way and Israel would have accepted Jesus as the Messiah then mankind would still be sin and eternally separated from God (Romans 6).  The parables of Jesus have also given us insights into spiritual matters that we would not be able to understand any other way (Matthew 13:14).  Parables have become a very important tool for us to understand many doctrines of the Bible.