Although one would think that a single reading would allow anyone reading it to define it in the same way as others, this is not always the case. In order to understand why this happens, one must understand meaning.
Any word has at least two meanings: a denotative meaning and a connotative meaning. A denotative meaning refers to a dictionary definition. A connotative meaning refers to the subjective meaning a person brings to the word (based upon emotions, prejudices, and experiences).
Therefore, when two different people read the same text, their connotative meanings can differ so greatly that each pulls a different meaning from the text.
In some cases, meaning arises based upon one's attitude toward a subject. For example, consider the highly controversial subject of abortion. Regardless of what the text states, a proponent of abortion will get a completely different message than an opponent of abortion.