What’s Up With the Title?
The Soldier. It's not "a soldier," but "the soldier," as in "the soldier, par excellence," or "the ideal soldier." That, at any rate, is what Brooke's title seems to be telling us his poem is about: a generic but ideal (or model) soldier, one who understands that he may die but also believes his death will benefit his country (England). As a result of his sacrifice, after all, "some corner of a foreign field" will be "forever England," no matter what happens.
To a certain extent, Brooke's poem reflects what many Europeans at the time would have considered an ideal soldier—one who loves his country very deeply (the words England or English occur six times in this very short poem). That soldier would also see his own death as a sacrifice that will benefit his country. And what's his reward for this sacrifice? Well, it's nothing but good times and high fives in the afterlife, that's what! The soldier's death is portrayed as not really the end, but only the beginning of a new, blissful, but (importantly) familiar life in heaven. So, this poem seems to be saying, let's all hear it for… The Soldier.