Both play minor, but extremely important supporting roles in these scenes. Friar Laurence, on the surface, becomes Romeo's confidant, advisor, and facilitator. He will be the one to guide the couple into marriage. He is first introduced in scene 3, picking herbs. This foreshadows the significance potions and poisons will have in Act 5. Also, he is soliloquizing on the essential duality of humanity. He ponders how one plant can contain the power to both heal and kill, & he compares that the potential for good and evil in a man. This may foreshadow the good and evil that will appear in multiple characters. Indeed, it suggests that this play is not one of black and white: each character has levels and shades of morality. He himself chastises Romeo for rushing into love; he then agrees to marry Romeo & Juliet without really giving it any thought. His intentions are good (he wants to end the feud between the families) but his own rush to help may turn out badly.
The Nurse plays a similar role, although she takes more pleasure in the secretive nature of the arrangement. She also plays the role of Juliet's protector, warning Romeo against hurting her. She is closest to Juliet and enjoys being a part of the romantic plans of marriage. She is the important messenger of the details of the union, of when and where it will take place. She and her attendant Peter find Romeo lounging with his friends on the streets of Verona. After exchanging bawdy jests with Mercutio (which ends with her being rather upset), she finds Romeo & tries to act important. However, she continually mixes up words, which shows that while she may attempt to put on airs, she cannot disguise her true nature.
In Act III, Scenes 3 and 4 of Shakespeare's "Romeo and Juliet" both Friar Laurence and the Nurse are catalysts to the tragic fates of Romeo and Juliet and others, as well. For, had they not become complicitous in Romeo's plans, the marriage would not have taken place, at least not with such celerity. Then, too, Romeo would not have told Tybalt that he loved him in the street when the young man is so distempered if he had not married Juliet. Without Romeo's remark which incensed Tybalt, Mercutio and he may have just continued to bandy words and not have drawn swords.
The duplicity of the Nurse and Friar Laurence is most unexemplary, as well. Both adults are in positions in which they should wisely advise the young people to respect their parents. Yet, Friar Laurence, especially, steps outside the bonds of his station in life when he agrees through subterfuge to marry the young couple. For, he is a friar, one of an order that takes the vow of humility. On the contrary, his act of surreptitiously marrying Romeo and Juliet without the consent of the parents is one of overweening pride: Friar Laurence believes his act will effect a solution to the feuding of the families. However, in his arrogance, he is wrong; in fact, he is the most responsible for the death of the two young lovers.
Similarly, the Nurse forgets her position of maturity and immerses herself giddily in subterfuge. Shortly after Juliet is married, Lady Capulet urges her daughter to marry Paris. Aghast after her mother leaves, Juliet seeks comfort from the Nurse; instead the Nurse tells her to marry Paris, knowing that Juliet cannot do this. Unwisely, she advises Juliet to marry Paris, saying,
Faith, here it is,/Romeo is banished, and all the world to nothing/That he dares ne'er come back to challenge you;/Or if he do, it needs must be by stealth. (III,v,214-216)
Her words, suggesting bigamy, upset poor Juliet so much that the young woman contemplates suicide, and later turns to Friar Laurence, becoming a part of his desperate plan to reconcile the families. However, his "best laid plans" do not work as his message does not reach Romeo before he enters the tomb and discovers Juliet as she lies "dead." Impetuously, Romeo takes the poison and dies in the arms of his young wife. Truly,the poor judgment of the Nurse and Friar Laurence serve only to ignite the fire of the impetuosity of the two star-crossed lovers, Romeo and Juliet.