Jesus is the greatest teacher and communicator ever seen. His ideas and thoughts were full of life and imagery relevant to his culture.
Imagery is a key.
The human mind loves to discover for itself rather than being force-fed. Through the use of imagery we have the opportunity to enable the audience to draw out for themselves their own truths. Through this one comparison we can see how an argument may be small to start with, but it will grow and become more and more destructive. Like a small hole in a dam, it grows till finally it destroys all life near the dam and the dam is left empty. Some of these parables were mysteries to the crowds that gathered.