How we cite our quotes:
It seemed that out of the battle I escaped
Down some dull tunnel, long since scooped
Through granites which Titanic wars had groined. (1-3)
Our poor speaker is temporarily duped. He thinks he's finally escaped from the horrors of warfare. But of course he's never going to be able to escape because they've followed him to hell. This passage to hell—or tunnel—seems to have been carved out of the mess past wars of left behind. Owen seems to be trying to tell us that these wars, even if they're over now, seem to have left their impact on the world in a serious way.
Yet no blood reached there from the upper ground,
And no guns thumped, or down the flues made moan.
"Strange friend," I said, "Here is no cause to mourn." (12-14)
This one's a real kicker. You can almost feel the speaker breathing a sigh of relief. For a brief moment, because he's not in the thick of battle, he thinks he's safe—even though he's in hell now.
[…] I meant the truth untold,
The pity of war, the pity war distilled. (24-25)
Looks like if there's one lesson to learn in hell, this is it: war's a complete and utter shame. It is, itself, a pity, and it causes pity. It's not good for anybody or anything, under any circumstances, capisce?