First, from Franz Kafka's "On Parables":
Many complain that the words of the wise are always merely parables and of no use in daily life, which is the only life we have. When the sage says: 'Go over,' he does not mean that we should cross to some actual place, which we could do anyhow if the labor were worth it; he means some fabulous yonder, something unknown to us, something that he cannot designate more precisely either, and therefore cannot help us here in the very least. All these parables really set out to say merely that the incomprehensible is incomprehensible, and we know that already. But the cares we have to struggle with every day: that is a different matter.
Concerning this a man once said: Why such reluctance? If you only followed the parables you yourselves would be parables and with that rid of all your daily cares.
Another said: I bet that is also a parable.
The first said: You have won.
The first said: You have won.
The second said: But unfortunately only in parable.
The first said: No, in reality: in parable you have lost.
(From The Complete Stories by Franz Kafka, page 457)
Second, two sections from Matthew 13:
He replied, “Because the knowledge of the secrets of the kingdom of heaven has been given to you, but not to them. Whoever has will be given more, and they will have an abundance. Whoever does not have, even what they have will be taken from them. This is why I speak to them in parables:
"Though seeing, they do not see; though hearing, they do not hear or understand."
“I will open my mouth in parables, I will utter things hidden since the creation of the world.”
|Christ on the Cross Between Two Thieves by Rubens|
I think it's safe to say that while much of our culture values clarity, far fewer people value mystery, especially when it comes to speech. Kafka is famous for being difficult to understand, but this comes from his stylistic commitment to mystery. Even when we examine Christ's speech, we notice two different types of speech. The first is mysterious, and intentionally so. The second type is explanation, but explanation is reserved for those who follow.
Parables are works of art, and while I wouldn't try to explain art solely through parables, I think that parables teach us about types of art beyond the mere genre of parable. Parables, as illustrated in all three passages, are inherently secretive and hidden, mysterious, but I don't think this is their defining attribute. While you could argue that Jesus is merely trying to confuse people, I believe he has a deeper purpose. We are called to seek an answer, an answer only found in the sacred. Parables are mysterious because they speak towards the sacred. The sacred can be found, but it cannot be presented. It must be sought. The ability to understand parables is not a question of ability but of faith, and by faith I mean a humility and trust that commits us to a God who is truly sacred. Art is a leading for the seeking; art is a sign to the sacred.