The purpose of Henry's speech is to persuade his audience to take

action. What specific action does a Henry urge his audience to take?

why do you think that precise purpose of Henry's speech only becomes clear in the second half of the speech rather than the first?

The actions that Henry urge his audience to take is first to judge their future based on their earlier lives. When they do this, then they will have hope of future reconciliation.

Another action he wants them to take is considering being in a stronger position since the British chains are moving closer as well as entangling the colonialism each day.

Explanation

Henry's speech is famous in the second part because people get to realize what exactly he is saying, and they are ready to emulate his actions.

This will enable them to be active instead of standing idle while the rest are fighting for freedom.