People can't concentrate properly on blowing other people to pieces if their minds are poisoned by thoughts suitable to the twenty-fifth of December.

In Nash’s characteristically barbed, comic diction, the line juxtaposes the bureaucratic logic of war (“concentrate properly”) with the moral and emotional associations of Christmas (“thoughts suitable to the twenty-fifth of December”). The joke turns on calling humane, peaceable sentiments a “poison” to the war effort, exposing how militarism depends on suppressing empathy and fellow-feeling. By framing violence as a task requiring focus, Nash satirizes the dehumanizing language that makes killing sound like ordinary work. The quote functions as an antiwar epigram: if people are allowed to dwell on ideals of goodwill and charity, organized destruction becomes harder to justify or carry out.