It was written in order to recreate the spirit of the original books of the New Testament, which were written in the street language of the day. The Greek language has two levels: formal and informal. If someone were to write something intended for posterity, they would write in the formal language. Formal language was used for things such as philosophy, law, history, and epic poetry. However, the New Testament was written in the informal language, the everyday speech of the common people.
The Message was written as an attempt to return to that, to convert the Bible back into the language in which we think and speak. Peterson notes that in the course of the project, he realized that this was exactly what he had been doing in his thirty-five years as a pastor, "always looking for an English way to make the biblical text relevant to the conditions of the people."