As themes go, this is the big one…but you knew that. (It's not called the "Give Me Liberty or Give Me Death!" speech for nothing.)
The speech is an argument for taking up arms in the cause of freedom from tyranny. Henry hits again and again on the idea that Britain's policies are oppressive and are designed to limit colonial freedoms to the point that the colonists will ultimately be unable to resist. Throughout the speech, he'll address other issues, but he always brings his points on home to this idea of freedom from tyranny.
That final line says it all: death is preferable to living without freedom.
Henry holds Lord North and Parliament most to blame for current oppressive British policies.
If you asked him, Henry might not be able to tell you exactly what he means by "freedom" and "tyranny." He's throwing highly charged words around to get an emotional reaction from his audience.
The war hasn't actually started yet, so in "Give Me Liberty or Give Me Death!" Henry's dealing with war as a hypothetical idea.
Because the goal of his speech is to convince the Second Virginia Convention of the need for raising a militia, Henry's heavy on the idea that fighting is coming, and in fact, at this point, given everything else Henry and Co. have tried, it's the only option left. In the speech, we see war as the ultimate result of a failure of diplomacy.
Talking it out failed, so now it's fight-time.
Henry's call to arms is an emotional appeal meant to cause his listeners to ignore logical arguments against it.
Henry's call to arms is based primarily in logical arguments with little reliance on emotion.
And by "hope" we mean "total and complete utter lack of hope."
When Henry's not talking about freedom and tyranny or about warfare, he's talking about how little hope he has that Great Britain and the American colonies can ever come to a peaceful resolution of their problems. Henry has to take a swipe at that best and worst of all emotions— hope—because hope is the main thing standing in the way of the Second Virginia Convention taking decisive action and voting to form militias.
Nobody in their right mind wants war, and he knows as long as they have hope war can be avoided, they'll keep trying to avoid it.
Henry's scorn at the idea of hoping for a reconciliation with Great Britain makes those who think one is possible feel super naïve.
Mocking the idea of hope allows Henry to persuade those who still have hope that Henry is in the right.