Patrick Henry uses anaphora, the repetition of a sequence of words at the beginning of sentences, when he describes how the colonies have attempted to negotiate with their sovereign: 

We have petitioned; we have remonstrated; we have supplicated; we have prostrated ourselves before the tyrannical hands of the ministry and parliament.

Henry points out that the colonies have tried peaceful, civil negotiations, and even uses exaggerated (hyperbolic) imagery to suggest that they have thrown themselves on the floor and begged for fair treatment.

Henry again employs anaphora to describe what Britain's response to the colonies has been:

Our petitions have been slighted; our remonstrances have produced additional violence and insult; our supplications have been disregarded; and we have been spurned, with contempt, from the foot of the throne.

His emotionally-charged language describes the dismissive attitude of the British in response to the colonies' attempted negotiations.

Henry once again uses anaphora  when he asks rhetorical questions to anticipate and counter the objection that the colonies do not have a military mighty enough to engage in a war against Britain.

Shall we gather strength by irresolution and inaction? Shall we acquire the means of effectual resistance by lying supinely on our backs, and hugging the delusive phantom of hope, until our enemies shall have bound us hand and foot?

Anaphora is a type of parallel structure that is particularly effective in speeches because of its rhythmic quality. Anaphora offers the additional benefit of making points more easily remembered.