I'm always curious and intrigued when Halloween rolls around to see all the different costumes people choose to wear.  Some represent cultural expectations like the little girl who dresses as a princess while the little boy dresses like a superhero.  The modern adaptations of the festival itself skew the selections toward ghouls, witches, vampires and the like.  Yet, for the most part, people are very particular about the costume they pick that represents their desire of who they want to be portrayed as for this night.  In other words, what alter ego someone picks to mask their true nature, if even for an evening's worth of candy collection or mischief making, is carefully chosen for specific reasons and not a choice arbitrarily made.  Thus, while the costume acts as something that conceals the true identity of the wearer, it nevertheless also reveals something about the wearer's desire in how they want to appear to others.  That is, the costume is both symbolic of a deeper, hidden reality (the person behind the mask) while at the same time used to conceal that reality.

This is exactly how Jesus uses parables and the reason he uses them: to communicate deeper, hidden realities behind everyday things that nonetheless are representative of God's presence.  But they are not arbitrarily chosen either; he carefully uses symbolic metaphors to conceal the information he seeks to convey from those to whom it does not pertain.  We often do the same thing: whenever you begin a statement with the words, "It's just like..," you are speaking parabolically because, often, we just can't get it if told to us straight.  We can only grasp the deeper, hidden reality behind something if given to us symbolically.  We Christians practice this every time we look at a cross or put a bumpersticker of a fish on our cars.

He put before them another parable: ‘The kingdom of heaven may be compared to someone who sowed good seed in his field; but while everybody was asleep, an enemy came and sowed weeds among the wheat, and then went away. So when the plants came up and bore grain, then the weeds appeared as well. And the slaves of the householder came and said to him, “Master, did you not sow good seed in your field? Where, then, did these weeds come from?” He answered, “An enemy has done this.” The slaves said to him, “Then do you want us to go and gather them?” But he replied, “No; for in gathering the weeds you would uproot the wheat along with them. Let both of them grow together until the harvest; and at harvest time I will tell the reapers, Collect the weeds first and bind them in bundles to be burned, but gather the wheat into my barn.” ’

He put before them another parable: ‘The kingdom of heaven is like a mustard seed that someone took and sowed in his field; it is the smallest of all the seeds, but when it has grown it is the greatest of shrubs and becomes a tree, so that the birds of the air come and make nests in its branches.’

He told them another parable: ‘The kingdom of heaven is like yeast that a woman took and mixed in with three measures of flour until all of it was leavened.’

Jesus told the crowds all these things in parables; without a parable he told them nothing. This was to fulfil what had been spoken through the prophet:
  ‘I will open my mouth to speak in parables;
   I will proclaim what has been hidden from the foundation of the world.’

Then he left the crowds and went into the house. And his disciples approached him, saying, ‘Explain to us the parable of the weeds of the field.’