"Compared to His earlier teaching during the Sermon on the Mount, Jesus's turn to parables might seem odd. He'd used clear instruction to teach His followers how to live and about the Kingdom of God, and He'd exhibited the Kingdom in a tangible way through His miracles. But suddenly, when the crowds come to hear Him, He hops into a boat and speaks in parables, stories about sowing seeds and gathering wheat (Matthew 13)." Read more from Alfred Edersheim.
When the disciples ask Him why, since they obviously noticed the change, His answer may seem even more astonishing: "To you it has been granted to know the mysteries of the Kingdom of Heaven, but to them it has not been granted" (Matthew 13:11). In other words, the parables are meant to divide the crowd. While this may seem as if Jesus denied some people access, the difference He means is not in the message—but in the response.