At this hour, what is dead is restless and what is living is burning.
Big Moment. In lines that echo the title (that's how you know this is a Big Moment, folks), our speaker expresses something like this: I imagine that the dead are restless, and I happen to be full of turbulent emotions right now, too, thank you very much.
Despite the fact that emotions are running high, our speaker communicates this in a rather detached way, as if simply listing a couple of facts. Plus, he avoids saying "I."
Who are these restless dead? Well the only dead person we have in the poem so far is the speaker's brother, who is quite restless, based on his description. He's rumbling around upstairs, slamming doors.
The narrator could be restless, too. After all, he's awake in the middle of the night.
And that burning also makes us think of the birthplace set to torches again, doesn't it? There sure is a lot of destruction going on.
Someone tell him he should sleep now.
Our speaker wants his brother to sleep, perhaps because he's sick of the noisy thumping upstairs, or perhaps because he wants his brother to find eternal peace. Hey, perhaps it's both.
The word "sleep" is the first official evidence that backs up our suspicions that this poem is taking place at night, and that "This Hour" is probably one of the very early hours of the morning – you know, the wee hours?
It's a strange thing to say, because it seems as though the speaker is the one who's restless, not someone else. He can't sleep, and stays up hearing creaks in the house and thinking of his brother. In a way, what he's saying might be: please quiet these thoughts of my brother so I can sleep.
There's also a sense of detachment from the brother. Our speaker asks for someone to "tell him," which suggests that our speaker himself can't tell his brother. Maybe that's because he's still alive (and therefore not with his brother in heaven), or maybe he just doesn't have the courage to do so. Maybe he isn't willing to admit to his brother that he'd rather he left him alone.
In fact, this line almost reads like a prayer, only it's directed vaguely to "someone," rather than specifically to God. Please, someone, tell my brother to pipe down.