The preamble of the Constitution is as follows.
"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."
In these days of partisan politics, of debate over what government should do, and how big it should be, it might be a good idea to look at this sentence again.
The Constitution, as set out above, tries to accomplish six things. For the next six days I will write about each goal.

The first thing the Constitution sets out to do is to achieve a "more perfect Union". NOT a Union - that was already achieved by the Articles of Confederation of 1777. The Constitution, in 1788, set out to do more.
Think about the times. If you think the current sate of the Union is fractious, with red states and blue, imagine what it was like in 1777, trying to join together the Quakers of Pennsylvania, the Puritans of Massachusetts, the free thinkers of Connecticut, the huge company town that was Virginia, and Georgia, which had been founded specifically as a place where the poor and indigent of England could find land.
The Constitution was formed, not as a compromise, but as a promise. It was a framework that would allow all these groups to cooperate for their own good, in order to stave off the powers that would have preyed upon them, and those that did. Many forces conspired against the thirteen colonies in the early years, from Barbary Coast pirates to European businessmen. They needed to stand together, even while detesting each other.
If you cannot see the parallels of today, then you are truly blind. There are as many enemies awaiting their chance to strike America as there were in 1777. And America is just as divided. But it is still possible for Americans to work together. It is possible to say "You're a liberal, and I think you're brain-dead, but I will let you think the way you do, and together we will live in safety". It is possible to say "You're a neo-con, and I think you're incompetent, but I will let you go on living your life as I go on living mine, and together we will beat back our common enemies".
That was the first goal of the Constitution of the United States of America.