ANSWER: Parables, particularly those given by Jesus, are stories or illustrations that use objects, situations and so on that are common to man in order to reveal important principles and information. Nelson's Illustrated Bible Dictionary defines parables as a short, simple story designed to communicate a spiritual truth, religious principle, or moral lesson; a figure of speech in which truth is illustrated by a comparison or exampled drawn from everyday experiences.
Some parables of Jesus are short, such as those labeled the Hidden Treasure (Matthew 13:44), the Great Pearl (verses 45 - 46), and the Net (verses 47 - 50). These, and some other parables given by Jesus, are not so much extended moral stories, as they are illustrations or figures of speech.
Although Jesus is the best-known person in the Bible for using this teaching tool, it also appears frequently in the Old Testament. For example, Nathan first confronted King David by using a parable concerning a ewe lamb in order to condemn him obliquely initially for committing adultery with Bathsheba and killing her husband Uriah the Hittite to cover up what he did (2Samuel 12:1 - 4).
By using experiences drawn from the world to make spiritual or moral points, Jesus could make some of His teachings a little clearer and vivid. For example, consider the very famous story of the Good Samaritan (Luke 10). An expert in Jewish law came to Christ and asked what he needed to do to inherit eternal life (Luke 10:25).
After Jesus confirmed that he should love God with his whole heart and his neighbor as himself, the lawyer (wanting to justify himself) asked who their neighbor is. The Lord responded by speaking the Samaritan parable in order to convey that humans should possess a basic concern about the welfare of ALL people and not just their family, friends or those they live near.
Were they meant to evangelize?
Did Jesus use parables as just another tool to preach the gospel? Are they meant to give the masses the information needed for salvation? When his disciples were quite puzzled at the meaning behind his story of the sower and the seed they came to Jesus privately for an explanation. His response was the following.
"To you it has been given to know the mysteries of the kingdom of God; but to the rest it is given in parables, so that in seeing THEY MAY NOT SEE, and in hearing THEY MAY NOT UNDERSTAND" (Luke 8:10, HBFV throughout)
The point made in Luke 8:10 goes so contrary against popular opinion on this matter it is worth confirming by looking at a bit longer, parallel explanation in Matthew 13 of what Jesus stated.
And His disciples came to Him and asked, "Why do You (Jesus) speak to them in parables?" And He answered and said to them, "Because it has been given to you to know the mysteries of the kingdom of heaven, BUT TO THEM IT HAS NOT BEEN GIVEN . . .
And in them is fulfilled the prophecy of Isaiah, which says, 'In hearing you shall hear, and in no way understand; and in seeing you shall see, and in no way perceive . . . (Matthew 13:10 - 11, 14).
To reveal and conceal
So, does Jesus contradict himself? How can this teaching method both teach and reveal principles yet also conceal profound truth? How do they teach important life lessons yet HIDE the knowledge needed for salvation? The answer lies in the fact that God has built into these stories two levels of meaning.
The first level is a basic, superficial understanding (which many times can still be misinterpreted) that the average unconverted person can comprehend apart from God. The second level, which is a deeper, more profound spiritual meaning that can ONLY be understood by those whose minds God has opened. Only those 'to whom it has been given,' according to Jesus, meaning those the Eternal is actively working with, can comprehend the profound spiritual truths parables discuss.
In the story of the Good Samaritan, the basic meaning the majority of humans draw from it is that they should be merciful and compassionate to people they do not know who cross their path in life. The secondary or deeper meaning, given to those God is working with, is that since He unconditionally loves everyone, believers must strive to do likewise.
According to Jesus, Christians are not permitted the luxury of not caring about the needs of others who they do not know. Believers are called to be perfect, even as God the Father is perfect (Matthew 5:48, Luke 6:40, John 17:23).
Why did Jesus use parables? He used them as a means to communicate two different messages, to two vastly different sets of people (those who are not and those who are converted), utilizing only one technique.