Answer:
The primary objective of the Declaration of Independence is to formally recognise Great Britain's retaliation against the United States and her failure to react to pleas as justifications for this decision. By addressing a higher power, it argues for the justice of their argument in an emphatic and forceful manner.
The Preamble to the US Constitution, in contrast, sets forth the aims and purposes of the new government, forming a more perfect union, justice, defence, and advancing the common good. Its more pragmatic and cooperative tone conveys the willingness to cooperate for a common goal. The Preamble has a more calm and even tone than the Declaration of Independence, which is more passionate and strong in its vocabulary.