What is the purpose of the phrase "establish Justice, insure domestic Tranquility, [and] provide for the common defence" in the Preamble to the U.S. Constitution?

A. To claim that the new Constitution can be changed over time
B. To explain that the U.S. government has a duty to protect its people
C. To guaranteed that the American people will get to vote on all new laws
D. To show that the people hold all political power in the country.