What is the most important part of the Declaration of Independence?

Of all of Jefferson's rhetorical techniques in the Declaration of Independence, perhaps the most important and persuasive inclusion is the litany of abuses of King George III of England.  
Jefferson structures a long run of parallelism with the repeated phrase "He has..." to enumerate very specifically what the king has done to hurt the colonies as well as the things he has not done to help them, ranging from denying the passage of laws that would be helpful to the colonies to stirring up domestic troubles in the colonies and inciting Native Americans to kill colonists without regard to the traditional rules of engagement.  This recitation of abuses offers a strong piece of inductive reasoning and a convincing rationale for separation.
Jefferson follows the litany of King George III's abuses with a statement that the colonies have tried repeatedly and in vain to resolve their differences with England in "the most humble terms."