The second stanza gives an example of the main theme of the poem. The “purple Host” that is being referred to is an army. The narrator explains that the army is unable to define “victory” because they are unaware of how loss feels. The soldiers cannot fully comprehend how great their victory was, because they aren’t aware of the devastation they would feel at their loss.
The third stanza
speaks of a one of the soldiers from the losing side of the battle. There is a large impression that he is dying while watching the enemies celebrate their victory. His loss of the battle is what causes him to have the ability to appreciate what a success would have meant. “Burst agonized and clear” is in reference to his strong want for the winning of the battle, now that he understand loss.
The poem being told from a third person point of view brings a detachment that would not otherwise be present. It is not clear if the narrator understands success, or if they have ever faced a loss like the dying soldier.