The poem is built from fragments, and that broken quality is part of its meaning. It begins mid-thought with a man "who was not for the war," then quickly complicates him: whatever he pretends, he "means no hurt in it." We never learn who he is. The speaker seems to be turning over an excuse, the kind people make for someone who disapproves of violence but goes along with it anyway.
The image of the "failed swan / coming home to a field" is the strangest and most moving moment. A swan belongs on water, so one in a field looks awkward and out of place, a bit defeated. It might stand for that man, or for the speaker.
The last lines bring things down to the ordinary: at the office, the speaker binds himself "to strict rules." The title, "Propriety," suggests that polite, orderly conduct can be a way of staying quiet. The mood is uneasy and quietly guilty, as if good manners and complicity were hard to tell apart.