Jefferson aimed to unite the colonists against the British government in writing the Declaration of Independence. The conclusion of the Declaration of Independence supported his purpose it stated that the document was approved and supported by the representatives from all thirteen colonies.
In the introduction, Jefferson first stated his purposes and then discussed the relationship between Britain and the colonies. He also explained the way by which the government should function.
Then, in the body of the Declaration, he explained how the English king was not fulfilling their expectations.
Jefferson did not tackle the topic of slavery in the Declaration of Independence as some colonies were favoring slavery while other colonies were opposing it, so it would have been difficult to unite them regarding this issue.