Why did Jesus bother with parables?

Why did Jesus bother with parables if, as he said in Matthew 13:13, They seeing see not; and hearing they hear not, neither do they understand?

Many years ago, in my youth, I used to do marathon walking, up to 50 miles (80 kilometres) a day. One evening I was walking at dusk, and just as I wondered if I was coming close to the next town, or whether I should rest on the side of the road until the morning, a motor vehicle drove past, headlights blazing, illuminating a reflective sign on the roadside ahead telling the distance to the next town. No, I hadn't seen the sign ahead in the darkness, but the reflected light from the vehicle was all that I needed for it to be visible. Jesus' parables were like that sign in the dark. Truth couldn't be seen until light was shed upon it. Truth was there, it just couldn't be seen. Jesus' parables are within our reading or hearing. We need the light of God's Spirit for us to be able to see them so that seeing we will see and hearing we will hear and understand.
-- Lionel Hartley.