Why do paine thought it was so important to have a written constitution

Thomas Paine believed that our God-given, inalienable rights can best be assured for all persons through the agency of a written constitution.  A written constitution details exactly how we together as citizens will respect and safeguard our own and one another's rights within the society we establish by our constitution.  A constitution also prevents a government that rules without the consent of the governed.

In an essay entitled, "Of Constitutions, Governments, and Charters," Paine asserted:  "A constitution defines and limits the powers of the government it creates. It therefore follows, as a natural and also a logical result, that the governmental exercise of any power not authorized by the constitution is an assumed power, and therefore illegal."