Every Biblical book is conditioned by the language, time and culture in which it was written. Because we are so far removed from that time, culture and language, we must work to understand it. In order to truly understand what God's word is to us, we need to understand what God's word was to the original audience.
Literary Context.
Far from teaching us that no private individual can correctly interpret the Bible, 2 Peter 1:20 ("no prophecy of Scripture is of any private interpretation") teaches us an important rule to be used by anyone who desires to understand the Bible. No single Scripture stands on its own. The Bible must be understood as a whole, with a single dominant theme, a unified message, and one Divine Author.
Scriptures cannot be understood out of context. Every word must be understood as part of its phrase; every phrase as part of its verse; every verse as part of its passage; every passage as part of its chapter; every chapter as part of its book; every book as part of its testament; and both testaments as part of the Bible. No true understanding of any portion of the Bible occurs when it is removed from its context.
One of the most common errors in using the Bible is the "hunt and peck" method of study. Rather than reading and trying to understand the entire message of the Bible, a person will string together several verses or short passages. These "key verses" are usually not chosen because they truly are key to the meaning and message of the books in which they are found, but because they strike an inner chord within the reader. It is not bad to have favorite verses or to memorize isolated passages, but when these passages loose their contextual meaning, they have lost all meaning.
A related error is the "proof text" method. A person will form an idea about God's position on a subject and will then quote a single verse or a selection of verses as proof. Often, if verses are found that seem to contradict the position, these are simply omitted from the list.