Why did the colonists find the writing of the Declaration of Independence so important for the creation of the United States?
This site will give you some insight.
But think of the declaration in these terms... Suppose you decide to quit school before you graduate, this will be a disaster to the people who have been in control of your life. You need to persuade them, explain, why this action is absolutely essential and further more justified. That is what the Declaration is...a justification of an "outrageous" action.