"Jesus spoke all these things to the crowd in parables; he did not say anything to them without using a parable."
Parable according to Webster means a short fictitious story that illustrates a moral attitude or a religious principle.
Jesus' disciples also asked this question.
"The disciples came to him and asked, 'Why do you speak to the people in parables?' He replied, '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 he will have abundance. Whoever does not have, even what he has will be taken from him. This is why I speak to them in parables: 'Though seeing, they do not see; though hearing, they do not hear or understand.''"
The Old Testament gives us some insight into the use of parables as well.
Godly Wisdom Allows Understanding - No Knowledge Without God
"Let the wise listen and add to their learning, and let the discerning get guidance -- for understanding proverbs and parables, the sayings and riddles of the wise. The fear of the LORD is the beginning of knowledge, but fools despise wisdom and discipline."
Proverbs 1:5-7 (926 B.C.)
The simple short stories that Jesus taught were wonderful moments that both perplexed and enlightened. Many occasions in the Bible explain how the Pharisees or Sadducees were stumped by what Jesus said or questions Jesus asked (Matthew 9:11-13, 15:1-14, 19:3-12, 22:23-34; Luke 20:27-40). Jesus' followers marveled at His wisdom and yearned to remain close to Him to soak up as many gems of wisdom that they could. Parable teaching was a brilliant mechanism to communicate with Jesus' followers and those sincerely interested in following Jesus, yet not communicate with Jesus' enemies. Also, parables were easier for people to remember and reflect on.