The theme of a poem is the message of the poem. Sometimes, a poem's theme is also an expression of the deeper meaning behind the words in the lines.

"They," by Siegfried Sassoon, is a poem that contains a powerful message, warning the reader about the limitations of religious faith. As well, the speaker of the poem is also conveying a vehement anti-war message characterized by frustration and anger.

In the first stanza of the poem, the Bishop attempts to glorify the actions of the young soldiers fighting in World War I. A bishop is often considered as an important figure of the church and here in this poem, the Bishop functions as a representative of religious faith. He describes the cause of the soldiers as "just" (line 3), and he celebrates the fighting by insisting that the soldiers have brought honor and more life potential to their own "honorable race" (5). But this point of view is limited, as the "boys" of the second stanza assert their exasperation with the Bishop's flawed platitudes about an experience that has damaged them physically, psychologically, and emotionally.

In the second stanza, the "boys" use plain language to describe their afflictions, which contrasts with the Bishop's elevated manner of speaking. Amputations, blindness, sexually transmitted disease are all mentioned in a straightforward way, emphasizing the hard reality of war. The Bishop is unable to appreciate these hard realities, and his inability to address the problems of the soldiers and to concentrate only on the honor and other intangibles highlights the limits of faith and religion.

The theme is how war dehumanizes us—both ourselves and the enemy. "They," the enemy, are no longer human beings; "they" are the anti-Christ and in fighting them we are fighting against evil personified. What is particularly disturbing about the poem is that it is the established Church which is peddling this particular line, sanctifying hatred between men. Christianity is supposed to teach fellowship of the soul, goodwill between men and women, and love for one's neighbor. Yet here a Christian bishop sees the war in apocalyptic terms, almost reveling in the hatred unleashed by this cosmic showdown between the forces of good and evil. The bishop too, has become dehumanized by the war.

The title also refers to the British soldiers who've come back from the war severely disabled. "They" too have been changed, but not in the way that the bishop means, not in the spiritual sense. "They" have been maimed, mutilated and physically wrecked by the conflict. Although supposedly fighting in a just and noble cause, they too have found themselves dehumanized. In the overall scheme of things, there is no real distinction in war between bishops, disabled veterans, and the enemy. "They" are all pretty much the same.

Siegfried Sassoon was a British poet known for writing anti-war poetry of World War I. This poem is an example. There are two stanzas, written in iambic pentameter, although with an irregular rhythm, and the rhyme scheme is: ababcc, dedeff.

There is religious imagery in the poem. In the first stanza, it says:

The Bishop tells us: 'When the boys come back
'They will not be the same; for they'll have fought
'In a just cause: they lead the last attack
'On Anti-Christ; their comrades' blood has bought

This means that a religious leader, the Bishop, has warned that when the soldiers come back from the war, they will be changed. They will have faced death. The enemy is perceived as "the Anti-Christ." This is a satiric comment indicating that the soldiers or their leaders have depicted the enemy as evil to justify the war. The speaker in the first stanza is an omniscient author.

In the second stanza, however, the soldiers speak:

'We're none of us the same!' the boys reply.
'For George lost both his legs; and Bill's stone blind;

This stanza continues to list the other horrors suffered by the soldiers, to which the Bishop replies:

And the Bishop said: 'The ways of God are strange!'

The poet seems to imply that in order to justify war, we have to vilify the enemy, turn the enemy into "the Anti-Christ." The last line is a common statement used by religious leaders to explain things that cannot be explained and in this poem, is an indictment against war.