How do the Declaration's and the Constitution's preambles differ? how are they the same? The Declaration of Independence
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.

The constitution

we the people in order to form a more perfect union, establish justice and insure domestic tranquility. Provide for the common defense, promote the general welfare and secure the blessings of liberty to ourselves and our posterity. To ordain and establish this constitution, for the United Sates of America.