We don't know much about our speaker, except that he's really good at giving commands. And since he's giving commands to a bunch of instruments, we can almost picture him as a conductor. But as it turns out, he's conducting music that can't be controlled: the music of war.
At the beginning of the poem, our speaker is commanding the instruments as if they'll do what he says to do, but by the end, he has taken a step back – he knows that nothing is under his control. We're pretty sure this isn't surprising to him: just as he was urging the music to disrupt the lives of everyone around him, it has disrupted his own life, too.
In fact, the way we see it, the band (if it's a real band) is probably too far away to actually hear our speaker anyway. Instead, the only people who hear him are the "talkers" and "lawyers" and "mothers," peering out from windows and doorways. But that's okay: we're pretty sure this is his audience anyway. He's trying to get these people riled up.
We can't be sure what our speaker's stance is on the war: he definitely wishes the people around him would pay more attention to it, but he's also sensitive to the suffering that it causes. Basically, he's human, and like the rest of us, he's not quite sure what to think about war.