What do we mean when we say it today?
- We'll try this one more time before giving up.
- Oh, come on, give it another go.
- Let's take another crack at it.
That's what this phrase is saying. People who say it aren't usually marching towards a breach or invading another country. They're trying something as a last resort, one more time.
When we say this phrase today, we might be casually talking about trying something, but it has often been used in a more political manner. This and one of Henry's other speeches ("band of brothers") was used to encourage troops went into battle in World War II and Iraq.
The fact is this speech is pretty powerful. It encourages soldiers to fight for their country, even when it seems like they are against all odds. It's also made an appearance in an episode of Star Trek as an episode title. And what could be more powerful than that?