The Preamble
Original Text (excerpted)
When in the Course of human events, it becomes necessary for one people to dissolve the political bands which have connected them with another, and to assume among the powers of the earth, the separate and equal station to which the Laws of Nature and of Nature's God entitle them, a decent respect to the opinions of mankind requires that they should declare the causes which impel them to the separation.
In Plain English
Sometimes in history, a group of people has to break away from another country. When this happens, they should respect the world enough to explain why.
Historical Context
The preamble sets up the entire document's logic: independence requires justification. The phrase "Laws of Nature and of Nature's God" reflects Enlightenment thinking — that certain rights are universal, not granted by any king or parliament.