Answer:
If this had not been done, we would not have the government that we do. In fact, the Articles of Confederation described a different government in an equal level of detail, and those articles had also been ratified by the people. If the Articles had not been ratified, that government would not have existed. We wrote, and ratified the Constitution because we tried the Articles of Confederation and found that they did not work.
Without the constitution, we have nothing.
Without a Constitution of some kind you either have no government, or a crazy autocratic one.