Final answer:
By suggesting that Ophelia's madness is a sign of greater troubles.
Step-by-step explanation:
Gertrude's reaction in the excerpt from Act IV of Hamlet serves to advance the plot by indicating that Ophelia's madness is not merely an isolated incident but may be indicative of larger issues. Gertrude's observation of Ophelia's behavior, such as speaking in doubt and spurning enviously at straws, leads her to express concern. Gertrude's decision to have Ophelia brought in suggests a recognition of the gravity of the situation. This move heightens the tension and indicates that Ophelia's condition may be a manifestation of deeper troubles within the kingdom.
Furthermore, Gertrude's reflection on her "sick soul" and the line "each toy seems prologue to some great amiss" hints at a heightened sense of unease and foreboding. This introspection adds a layer of complexity to the plot, as it implies that there may be hidden machinations or impending tragedies yet to be revealed. Gertrude's characterization as feeling guilt and expressing concerns about the spillage of guilt contributes to the atmosphere of suspicion and foreshadows potential revelations that could impact the overall course of events in the play.
In summary, Gertrude's reaction not only addresses the immediate concern of Ophelia's madness but also hints at a broader narrative layer involving hidden troubles and potential conflicts. This nuanced portrayal serves to deepen the intrigue of the play, keeping the audience engaged and eager to unravel the complexities within the characters and the unfolding events.