Final answer:
The purpose of the rhetorical device used in this excerpt is to convey the speaker's frustration and exhaustion with the unsuccessful attempts to resolve the issues between the American colonists and Great Britain.
Step-by-step explanation:
The purpose of the rhetorical device used in this excerpt is to convey the speaker's frustration and exhaustion with the unsuccessful attempts to resolve the issues between the American colonists and Great Britain. The speaker, Patrick Henry, presents his ideas by using rhetorical questions and emphasizing that all possible approaches have been exhausted. He questions whether argument, entreaty, or supplication could bring about any new solutions or terms that have not already been tried.