Thomas Jefferson accomplished two primary things when he completed The Declaration of Independence: He brought to the forefront the type of government that the colonist wanted and exposed King George III as a ruler who felt he could continue to harvest and reaps the benefits of the colonies.
The Declaration... created a document which espoused the type of government that the colonists wanted--one based on equality and freedom. In addition, the decisions would be made by ordinary people not an elite set of aristocrats or royalty.
In addition, it became obvious that George ignored the document and felt that he and his armies could control and overpower the newly formed congress. The American Revolution came about because of the democracy that the people wanted. George picked the wrong fight.