The goal of the preamble was to outline the core ideas of the new American government.
The US Constitution replaced the Articles of Confederation as the set of laws used for the federal government. This new constitution would consist of several different parts, including the preamble.,
The preamble discusses how this new constitution was developed in order to form a "more perfect union." Along with this, the preamble also discusses how this new system of government will protect the rights of citizens, provide for a common defense (aka military), and ensure peace.