The main purpose of the Declaration of Independence was to: D. argue that a new government was necessary to protect the rights of the people.
Since the revolution has already begun, the Declaration set out to demonstrate WHY the colonists had separated from Britain and British rule. It was necessary to split from the British government because the British government did not have the best interests of the colonists at heart. Colonists decided that it was important to start a new government so that their rights would be protected.