‘In contrast to most of the parabolic sayings, such as not reaping figs from thorn bushes (Luke 6:43), the story parables do not serve to illustrate Jesus’ prosaic teaching with word pictures. Nor are they told to serve as vehicles for revealing truth—although they end up clearly doing that. Rather the story parables function as a striking way of calling forth a response on the part of the hearer. In a sense, the parable itself is the message. It is p 158 told to address and capture the hearers, to bring them up short about their own actions, or to cause them to respond in some way to Jesus and his ministry.’
Fee & Stuart, How To Read The Bible For All Its Worth, 4th ed., p157f.