Answer:
The United States was already a ‘Union’ of 13 States, (formed under the Articles of Confederation and Perpetual Union) among the the purposes of the Constitution was the creation of a document which contained a comprehensive agreement between the states regarding the powers ‘ceded’ to the ‘Federal Government’ and its ongoing role in ‘The Union,’ and the relationship between the States’ themselves as part of ‘the Union.’
So, if ‘the Confederation and Perpetual Union’ was, at least in theory, ‘perfect’ (even though created in an emergency situation), then the ‘Constitution’ which amended the ‘ Confederation and Perpetual Union’ to ‘iron out the kinks’ had to ‘in effect’ to make that union ‘more perfect.’
Explanation:
We the people of the United States, in order to form a more perfect Union, establish Justice, insure domestic Tranquility, provide for the common defense, promote the general Welfare, and secure the Blessings of Liberty to ourselves and to our Posterity, do ordain and establish this Constitution of the United States of America. (And then the actual Constitution follows.)
So...The writers of the Constitution wanted a government that better met their needs/desires. They wanted justice, domestic tranquility (meaning within the borders of the new nation), common defense, general welfare, the blessings (of liberty) for themselves and those who come after. They ordained and established this new nation with with the following constitution.
In order to make their needs/desires happen/In order to form a more perfect union (nation), the political body writing the constitution wrote the constitution to better meet their needs/desires.
