The purpose of the preamble of the constitution is to
a establish and maintain the sovereignty of individual states.
b describe and enforce the powers of the confederation government.
c introduce and explain the core ideas of the new government.
d define and distinguish the roles of domestic and foreign policies.

The correct answer is C introduce and explain the core ideas of the new government.

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 to ensure peace. This preamble (introduction) provides a brief background of what rights/laws were implemented in the body of the US Constitution.