1. Shift in Focus: The first four stanzas describe the speaker's youthful desire for a motorcycle, culminating in his desperate attempt to steal one. The fifth stanza then shifts focus entirely to the aftermath of his action, highlighting the consequences of his impulsive behavior.
2. Change in Tone: The poem's tone shifts from the youthful excitement and longing in the first four stanzas to a sense of despair and resignation in the fifth. The shift in tone emphasizes the seriousness of the situation and the speaker's realization of the gravity of his actions.
3. The Speaker's Transformation: The fifth stanza marks a significant turning point in the speaker's emotional journey. He is no longer the carefree, impulsive youth but a remorseful, introspective individual grappling with the weight of his choices. The stanza's isolation underscores this transformation.
4. Emphasizing Isolation: The isolation of the stanza also emphasizes the speaker's sense of loneliness and isolation after the theft. He is alone with his guilt and shame, separated from the world he previously inhabited.
5. Symbolism of the Darkness: The image of "the dark" in the fifth stanza serves as a symbol of the speaker's emotional darkness and the consequences of his actions. It also suggests a sense of alienation and separation from the world.
6. Dramatic Pause: The separation of the fifth stanza creates a dramatic pause, allowing the reader to reflect on the speaker's situation and the impact of his actions. It also creates a sense of anticipation for the final stanza, which offers a glimmer of hope.
In conclusion, the fifth stanza's isolation in "Fifteen" serves to create a dramatic shift in focus, tone, and emotional landscape, highlighting the speaker's transformation and the weight of his actions. The isolation also emphasizes the speaker's loneliness and the darkness he faces as a consequence of his choices.