Before reading through this poem, it's important to consider its context. It was published in a British newspaper early on in the First World War (1915). At that time, it was not yet compulsory for young British men to join the army—they still had a choice whether to volunteer or not. In hindsight Pope's poem, written before anyone knew the full extent of the horror and tragedy that was to spread its shadow over Europe, seems like a naive call-to-arms. It asks its target audience—young, able-bodied men and perhaps their family members too—to ask themselves if they possess the honor, integrity, and sense of duty to put their lives on the line for the good of their country.
Throughout the poem, the severity of war is played down—with conflict presented as something more like a game or a sport. This is an extended metaphor established by the title, which is also the first line of the poem. The poem uses frequent rhetorical questions—almost like an interrogation—to push its reader to decide whether they are up for the "fight" or, essentially, too much of a coward. The anaphora of "Who's/Who'll" adds to the poem's sense of urgency and insistence.
The extended sporting metaphor is appropriate in the sense that sport matches are often played between different countries—and here, for the British, the opponent is Germany. The caesura in the first line creates emphasis on this being the "biggest" game ever played, with the prize nothing less than control over the country's future (and the defense of other nations).
Line 2 describes the war as a "red crashing game of a fight," suggesting violence without giving any real sense of the terror that is to come—indeed, this almost sounds like modern-day sports commentary! Line 3 picks up on the sporting metaphor with "grip and tackle," two verbs associated with the popular game of rugby (a bit like American Football, but with fewer pauses). The first three lines make use of /a/ assonance, drawing a connection between "a" "game" being "played" and being "unafraid," subtly reinforcing the poem's argument that to do otherwise is an act of cowardice.
Line 4 then presents the alternative to joining up—"sit[ting] tight." This kind of juxtaposition takes place throughout the poem, usually following a pattern of three lines that talk up the supposedly fun side of war followed by one that suggests the utter boredom of staying at home. The poem's clear, steady rhyme scheme further adds to its predictability. The poem can be broken down into a series of quatrains, or four-line stanzas, that follow a simple ABAB rhyme pattern (here, "played" rhymes with "unafraid" and "fight" with "tight").
It's worth noting that many people—including young men—shared Pope's excitement towards the war. In 1914 (one year before this poem's initial publication), most Brits expected the war to be done by Christmas—and some people definitely did sign up out of a sense of adventure, unaware of the death, disease, and destruction that was to come.