The Nurse is a greatly significant character mainly because she is Juliet's number one confidant and without her assistance in getting Romeo and Juliet together, the plot could not be developed.
First, it is the Nurse who tells Romeo that Juliet is a Capulet, setting the stage for the star crossed lovers' endeavor to be together. Later, the Nurse acts as a messanger to receive word from Romeo if he truly intends to marry her and if so when and where. Therefore, she is the only one other than Romeo, Juliet, and Friar Lawrence who know of the forbidden vows. Finally, the Nurse is the only one on the Capulet side who understands the dilemma Juliet faces when her dad orders her to marry Paris. When the Nurse's adivses her to forget about Romeo and begin a new life with Paris, she feels furious, alone, and desperate enough to take the Friar's potion and fake her death.
Throughout the play the Nurse acts as the middle-man, the go-between that enables the conflict to continue rising toward the dramatic double suicide at the end of the play.