What happens
Juliet waits for the Nurse, who has been gone three hours with Romeo's answer. She frets that the old move too slowly to carry love's messages. When the Nurse finally arrives she is out of breath and maddening — complaining about her aching bones, changing the subject, refusing to get to the point. Juliet pleads. At last the Nurse relents and delivers the news: Romeo is waiting at Friar Lawrence's cell, and Juliet is to go there at once to be married. Juliet rushes off overjoyed, while the Nurse promises to fetch the rope ladder for that night.
Why it matters
The scene is built entirely on delay, and delay is the play's deadliest force. Here it is comic — a girl desperate for news, a Nurse milking the suspense. Later the same engine turns lethal, when a delayed letter and a few wasted minutes decide who lives. Shakespeare lets you laugh at waiting before he makes you fear it.
Juliet's impatience is also her clarity. While the adults dawdle, she knows exactly what she wants and says so. The play keeps giving its almost-fourteen-year-old heroine more directness and resolve than the grown-ups around her, and this scene is a warm, funny example of it.
The Nurse's teasing is affectionate, but it is also a quiet picture of the distance between them. The Nurse feels the marriage as gossip and aching feet; Juliet feels it as her whole life. They love each other and live at different scales — a gap that will crack wide open when the Nurse later tells her to marry Paris.