Early in his speech, Henry declares, "I know of no way of judging of the future but by the past." This is an entirely logical point; the future is unknowable, but in situations where a precedent has been established, conclusions can be drawn about the likely direction of events to come. Henry believes the British ministry will behave in predictable ways in the future based on how they have behaved in the past.
Henry also believes it would be naive to think Britain does not intend to use force against the colonies should they begin to rebel. To the people who believe that petitioning Britain is a legitimate strategy, he says,
"Ask yourselves how this gracious reception of our petition comports with these warlike preparations which cover our waters and darken our land."
His point is that the British navy and army are already in place in the colonies and that armed conflict is inevitable. To anyone deluded enough to think Britain might be quartering troops in the colonies and anchoring warships offshore as a show of force to anyone besides the colonies, Henry asks,
"Has Great Britain any enemy, in this quarter of the world, to call for all this accumulation of navies and armies?"
Although it not customary to answer your own rhetorical questions, Henry feels compelled to inform his audience "No, sir, she has none."