What is the authors purpose in patrick henry speech ?

To show the colonists that war with Britain was their only option.

Explanation:

Patrick Henry's speech was titled ''Give Me Liberty, or Give Me Death!''.

From the titled you can see that this speech had the intention of a radical idea: or freedom, or death (which mean we'll fight).

Also you can get the answer from the context, this speech was given to the Virginia convention, where they was debating whether send troops to fight or not.

Despite the overwhelming body of academic work on the civil war produced in the united states (and beyond) most of the american public (as well as the international audience) has been exposed to it through cultural texts such as novels, poems, songs, motion pictures, tv series, and documentaries.

Bis correct you are right