The Mission Statement of the United States of America

 We the People of the United States, in Order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defence, promote the general Welfare, and secure the Blessings of Liberty to ourselves and our Posterity, do ordain and establish this Constitution for the United States of America.

"We", that is, everybody belonging to a certain group.

"the People of the United States," that group being everyone "of" the United States.

 "in Order to form", the People of the US are trying, collectively, to form or create something.

That being "a more perfect Union," among other things according to the comma (",").  They weren't stupid or naive, since they knew that perfection did not come instantly, that it was something that needed to be worked towards.  Among the things they were working towards was a "Union", that is more than just a "we", but rather a group with shared values and goals and an understanding that they were all in this together.

"establish Justice," in its simplest form, Justice is everybody playing by and being held to the same rules.  The rules, though, can be flawed so that some privileged classes are more privileged by the rules.  This means that even justice can be a work in progress.

"insure domestic Tranquility," This also applies to all of the People.  If a subset of the People are not tranquil, then all the People are not tranquil.  Some people seem to believe that to insure tranquility in this case requires that that those who are not tranquil be eliminated from among the People.  But in most cases, very few people are willing to commit genocide.  That leaves the People the only other alternative of trying to work things out among everybody.  This does not guarantee that everybody will be happy with the outcome, but failure to work toward the goal insures more discord.

"provide for the common defence," Common defense means the defense of everybody, the People.  In other words, the People defend the People, not some privileged group among the People, but defending the Union of the People.  Thus, if one group within the People attacks another group among the People, then the attackers can be said to be removing themselves from among the People, are no longer a part of the People.

"promote the general Welfare," that is, the welfare of everyone, all of the People.  This suggests that one group cannot profit at the expense of another group without violating this principle.  

"and secure the Blessings of Liberty" if those "blessings" are the result of an individual or individuals achieving a result that improves their lives, these results must be restrained according to their negative effects on others, on the rest of the People.  Failure to do so is contrary to the previous clauses.  Perhaps "Liberty" is a term summarizing the previous clauses (a more perfect Union, Justice, defense

"to ourselves and our Posterity," "ourselves" being "the People", and recognizing the People's responsibility to the future, "our Posterity".  

"do ordain and establish this Constitution for the United States of America." In other words, to achieve the above goals, the following rules are created.