What purpose did the introduction to the declaration of independence service

The Declaration of Independence was a new and radical way to:
a) Start a country.
b) Establish that country with very definite principles about the relationship between government and the people. 

The purpose of the introduction to the declaration of independence service was:
"It indicated why independence was necessary".

 According to the declaration of independence, Government has the power to protect natural rights, but people can change their government if it fails to do so.