What passing-bells for these who die as cattle? (1)
Cattle? Shmoop can think of a few more flattering things to call fallen soldiers. You might be expecting something like "die as heroes." But in an Owen poem, there are no heroes, just senseless death. Yep, he was a real uplifting guy.
Only the monstrous anger of the guns. (2)
That one word "monstrous" does a lot, don't you think? It ensures that we understand that the awfulness of war isn't something natural or manageable. It's crazy and unbelievable and just plain horrible. The guns are a sort of monster, brought to life at the expense of the soldiers who must use them and die by them.
Only the stuttering rifles' rapid rattle Can patter out their hasty orisons. (3-4)
Only the sound of rifles can speak the soldiers' prayers. Which seems to be a way of saying that the soldiers have no voice, no way to express themselves but through shooting. As bleak as that sounds, that's their duty, after all, as soldiers. No wonder they're compared to cattle in the first line. These soldiers don't seem to be able to think for or express themselves.
The shrill, demented choirs of wailing shells; (7)
Ugh. Has any line ever sent more shivers down your spine? Artillery shells falling from the sky are terrifying enough already, but compare them to "shrill, demented choirs" and you have an ugly mixture of heaven and hell that's enough to start you quaking all over.