The Disciples asked Jesus, "Why do you speak to them in parables?"
Flannery O'Connor was famous for her reply when someone asked her, "Can you just tell me in one or two sentences what each of your short stories means?" "If I could have said it any more clearly, I would have!"
So also with the parables of Jesus - We often are tempted to seek the simple "moral" of the story or the simple "meaning" of the metaphor, but the purpose of the parable is to bring us to meditate on the deep truths contained therein.
Further, parables often bring an opportunity for conversion even for those who are most hard of heart.
Lastly, we consider how Jesus established the hierarchical Church by speaking in parables to the crowds, but explaining the faith more fully to his Apostles who would then teach the people after our Lord's Ascension. Further, notice that Jesus didn't write any book of the Bible, which indicates that he did not intend to teach "sola scriptura" or the "Bible alone" - the Bible itself comes from the teaching authority of the Church (and the New Testament was written by the first Bishops, the Apostles).
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