Purpose of Parables

Luke 8:9-15

9  And his disciples asked him, saying, What might this parable be? 
10  And he said, Unto you it is given to know the mysteries of the kingdom of God: but to others in parables; that seeing they might not see, and hearing they might not understand. 
11  Now the parable is this: The seed is the word of God. 
12  Those by the way side are they that hear; then cometh the devil, and taketh away the word out of their hearts, lest they should believe and be saved. 
13  They on the rock are they, which, when they hear, receive the word with joy; and these have no root, which for a while believe, and in time of temptation fall away. 
14  And that which fell among thorns are they, which, when they have heard, go forth, and are choked with cares and riches and pleasures of this life, and bring no fruit to perfection. 
15  But that on the good ground are they, which in an honest and good heart, having heard the word, keep it, and bring forth fruit with patience.