What happens
Juliet waits for night and for Romeo, longing in a soaring speech — "Gallop apace, you fiery-footed steeds." The Nurse arrives with the rope ladder but in a wailing heap, crying "he's dead," and for a moment Juliet thinks Romeo is the one killed. The truth comes out tangled: Tybalt is dead, and Romeo is banished for killing him. Juliet swings between horror at her cousin's death and fury, then fierce loyalty, toward her husband. She settles it fast — Romeo is her life, and "banished" is a word worse than ten thousand dead Tybalts. Grief-struck, she sends the Nurse to bring Romeo for one last night.
Why it matters
The scene opens at the play's highest pitch of joy and ends near its lowest. Juliet's "Gallop apace" speech is pure wedding-night anticipation — and Shakespeare drops the news of the killing into the middle of it. The collision of erotic excitement and a death sentence, inside one scene, is the play's method in miniature.
Watch Juliet reason her way through an impossible loyalty. For ten lines she condemns Romeo — "O serpent heart, hid with a flowering face" — then catches herself and chooses him over her own blood. It is the moment she fully leaves her family and becomes Romeo's wife in her own mind, before they have even spent a night together.
The word that breaks her is "banished," not "dead." She repeats it helplessly. The play has been speeding up, and here it shows what the speed costs: separation, not violence, is the real punishment, and the one the lovers cannot survive.