The speaker describes a small group of fighters heading out toward evening to meet the enemy. They look like people who have "taken leave of the world," as if they have already stepped away from ordinary life and its ties. The title, "Guerrilleros," suggests irregular fighters, though the poem never says where or when this happens.
The strangest moment comes at the end. The group goes out "just as the great difference / between us was in doubt." The "us" is unclear. It could mean the fighters and their enemy, or the fighters and the people they have left behind. Either way, the line suggests that the gap between the two sides is blurring, and that the cause they believed in may no longer feel so certain.
The mood is quiet, dreamlike, and uneasy. Evening light, the loose phrasing, and the lack of any action all give a sense of drifting toward something unavoidable, with the speaker more unsettled than brave.