This is one of Sassoon's most cynical poems. Sassoon opposed the war so violently that he threw his Military Cross into the Mersey in protest and was sent to a convalescent hospital after a military court decided that he was out of his mind with neurasthenia, or "shell-shock." Sassoon's conviction that the war was an unjust one often manifested itself in anger against civilians, whom he felt could not understand—and often did not seem to want to understand—what was really happening on the Front. The title of this poem, "They," is an expression of this distinction Sassoon draws between soldiers and those at home: them and us.
The words of the Bishop in this poem, then, are a parody of what Sassoon and other returning soldiers had heard from the pulpit. The regular, almost childlike rhythm of the poem is reflective of the idea that this is, for the clergymen of Great Britain, purely patter. They do not really know what they are talking about, but bombastic, cliched phrases such as "just cause," "honourable race," and the concept of having "challenged Death" are utilized regularly to encourage patriotism at home. To the Bishop, and all others who are unfamiliar with the real state of affairs, the enemy is "Anti-Christ."
The soldiers, however, know better. The enemy are only men like them, and there is nothing honorable about this war. In forthright, robust terms, the soldiers list what transformations they have actually undergone as a result of their endeavors; they have lost their limbs, gone "stone blind," and even become "syphilitic." (This line in particular stirred criticism at the time of publication; it was considered an affront to the war effort to refer to soldiers' use of prostitutes.) The soldiers put their case very clearly to the Bishop, but he does not want to hear it -- instead, he simply says, in the same euphemistic tone, "the ways of God are strange!"
The poem is an expression of frustration on behalf of soldiers who have suffered in what Sassoon considered a greatly unjust war, and whose supposed spiritual leaders at home not only refuse to acknowledge their reality, but also continue to promulgate lies about the "honor" of war.