The correct answer to this open question is the following.
I would rewrite the text in the following way:
"We are the citizens of America and we want to establish a better nation. One country where justice is the basis of our government, that can also guarantee peace, protection, and prosperity for all, from here to eternity. These principles are the foundation of the Constitution of the United States."
What the founding fathers and the framers of the Constitution meant by the main phrases is the following.
We the People(the US citizens are speaking) of the United States, in order to form a more perfect Union(the goal is to improve the establishment of a new country), establish Justice(guarantee proper laws to everyone, including the government), insure domestic Tranquility(establish peace in the territory), provide for the common defense(protect the people from any invasion), promote the general Welfare(create the economic conditions for everybody to grow), and secure the Blessings of Liberty(guarantee that liberty will always be protected under any condition) to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.