Line one of paragraph two uses an interesting word choice "An ecstasy of fumbling" it's as if Owen was in such a state he saw his surroundings in slow motion. He describes one man, "As under a green sea, I saw him drowning (line 6 paragraph two)." I cannot imagine being in such an experience as that and Owen's words paint me vivid pictures.
The last paragraph is full of bitterness and irony, "The old lie: Dulce et decorum est Pro Patria Mori (line 11 paragraph 4)" meaning it is a sweet and honorable thing to die for ones country, is dripping with it. Lines 8-12 forewarn and say that if you saw what he had, you would not proclaim with such pride "to children ardent for some desperate glory (line 10 paragraph 4)" as in young, full spirited men who wish to fight simply because they feel it is glorified; because he truly knows what war is, and it is not glamorous or glorified but a vile and evil thing which brings nothing but haunting dreams and pain.