Answer :
"We the people of the United States, in order to form a more perfect union...." is an important quote because it is the opening of the U.S. Constitution and it seeks to explain the purpose of the U.S Constitution. It is called the "Preamble."
The cited quote is the Preamble of the United States Constitution. It is important because it introduces and explains the purpose of the U.S. Constitution.
The Preamble to the Constitution of the United States is a brief introductory statement of fundamental declarative and introductory principles of the US Constitution. It establishes general terms and objectives that the courts use as a faithful reference to the intentions of the Founding Fathers regarding the meaning of the Constitution and what they expected it to achieve.