Final answer:
The significant line of dialogue from the play "Trifles" by Susan Glaspell is spoken by Mrs. Hale and emphasizes Minnie Foster's past joy and current troubled state.
Step-by-step explanation:
In the play "Trifles" by Susan Glaspell, the significant line of dialogue is spoken by Mrs. Hale.
She says, "I wish you'd seen Minnie Foster when she wore a white dress with blue ribbons and stood up there in the choir and sang."
This line is significant because it highlights the contrast between Minnie's past joy and her current troubled state, indicating the impact of her husband's treatment on her life.