The Soldier is Petrarchan sonnet (or Italian Sonnet if you prefer.) This means it has 14 lines which are separated into stanzas. The rhyming pattern for this is typical of a Petrarchan sonnet, being ABBAABBA CDECDE. It is full of positivity and seems to glorify the idea of a person dying for their country. Due to its powerful convictions it is a poem that remains quite popular with military enthusiasts and as such has found its way into popular culture featuring in the music of Pink Floyd and Muse and finding its way onto television screens by appearing in the TV show MASH.
This is a sonnet based on the two major types of the sonnet: Petrarchan or Italian and Shakespearean or English. Structurally, the poem follows the Petrarchan mode; but in its rhyme scheme, it is in the Shakespearean mode. In terms of the structure of ideas, the octave presents reflection; the sestet evaluates the reflection. The first eight lines (octave) is a reflection on the physical: the idea of the soldier’s “dust” buries in a “foreign field.” They urge the readers not to mourn this death, though they implicitly also create a sense of loss. The last six lines (sestet), however, promise redemption: “a pulse in the eternal mind…. under an English heaven”. The rhyme scheme is that of the Shakespearean sonnet: the octave and the sestet consist of three quatrains, rhyming abab cdcd efef and a final rhymed couplet gg. As in Shakespearean sonnets, the dominant meter is iambic.
So now for the big question: why did Brooke use two different types of sonnet in the poem—one historically associated with England, and one with Italy? It may have something to do with the politics of the looming war, we think. It's not that England and Italy were fighting yet (that didn't happen really until World War II). But England was about to enter a conflict that began (and would be fought) on the European continent. In joining these two sonnet forms together, then, Brooke's poem is in a way enacting the kind of English-European fusion that was to come (only through arms this time, not words).