The unconscious mind can extract information from language through a derivational process. This allows us to extract more meaning from language then is actually signified by the language.
For example: The broken window Conveys not only that there is a window, and it is broken; but also implies the act of breaking which occured in the past, and had a culprite (who broke it? when?).
By using allegory without directly mentioning the client we can subvert the conscious mind and allow the unconscious mind to extract relevant meaning.
People can find it easy to learn => Implies people, and the unconscious mind can then make the connection- "I am a person, I can find it easy to learn" without the hypnotist having to directly speak to the conscious mind.
References
The Patterns and Techniques of Milton Erikson, Bandler and Grider, pg 222