Having explained Juliet's father's opinion, Paris says, "Now do you know the reason of this haste" (4.1.15). But the Friar knows--and we do, too--that Juliet's father's opinion explains nothing, and the Friar says to himself, "I would I knew not why it should be slow'd" (4.1.16). He can't tell Paris the real reason why the wedding plans should be delayed, and he wishes he didn't know that reason. As the Friar is thinking about the bind he's in, things get more complicated--Juliet appears.
As soon as he sees Juliet, Paris starts being obnoxious. His idea of wooing her is to tell her, over and over again, that she already belongs to him. Juliet has to fend him off without raising any suspicions about the true state of affairs. Thus a dialogue ensues in which Juliet skillfully keeps Paris at arm's length while allowing him to think that she's only being coy. Paris greets her by saying, "Happily met, my lady and my wife!" (4.1.18), to which Juliet replies, "That may be, sir, when I may be a wife" (4.1.19). He probably thinks she is teasing him by saying that they may be happy to see one another when they are married; her hidden meaning is that she will never be married to him and never happy to see him. Paris then says, "That 'may be' must be, love, on Thursday next" (4.1.20), and Juliet replies, "What must be shall be" (4.1.21). He hears her saying that she will marry him; we hear her say "whatever!"
Blind to Juliet's true attitude towards him, Paris assumes a possessive attitude towards her. He asks her if she has come to Friar Laurence to make confession, and she, using the word "confess" in its secular sense, answers "To answer that, I should confess to you" (4.1.23), which comes very close to telling him to keep his nose out of her business. Paris, however, is so sure of himself that he says, "Do not deny to him that you love me" (4.1.24), to which Juliet wittily replies, "I will confess to you that I love him" (4.1.25). In other words, the only confession of love that he's going to get out of her is a confession that she loves her priest, which sounds scandalous, although we can assume that she really does love Friar Laurence in the purest Christian sense. Paris tries again, telling her he's sure that she will confess her love of him to Friar Laurence. She answers, "If I do so, it will be of more price [value], / Being spoke behind your back, than to your face" (4.1.27-28). This is a nice way of telling him that he's certainly not going to hear her say that she loves him.
Paris now notices something which he might have seen before if he weren't so self-involved--that Juliet has been crying. He says, as though she were already his little wife, "Poor soul, thy face is much abused [ruined] with tears" (4.1.29). Juliet answers that her face was bad enough before the tears came, and Paris--trying to be the gallant lover--says, "Thou wrong'st it, more than tears, with that report" (4.1.32). In other words, by saying her face looks bad, she's doing it more harm than the tears have done. Juliet's reply reveals her irritation with her would-be husband: "That is no slander, sir, which is a truth; / And what I spake, I spake it to my face" (4.1.33-34). In this, Juliet asserts her ownership of herself. Paris has been saying that she has a beautiful face ruined by tears, and that she has been slandering her own face by denying that he is right. Juliet now says she 's the one who knows the truth about herself, and the one who can tell that truth to herself. Paris, however, contradicts her assertion: "Thy face is mine, and thou hast slander'd it" (4.1.35). The man is impossible, and Juliet lets him think what he wants: "It may be so, for it is not mine own" (4.1.36). At the same time, we can understand that her face is not her own because she has put on a face for the benefit of a man she detests.
At this point Juliet cuts the conversation short by asking Friar Laurence if he has time to hear her confession. He says he does, and she tells Paris she needs the time alone with Friar Laurence. Paris answers, "God shield [forbid] I should disturb devotion! / Juliet, on Thursday early will I rouse ye: / Till then, adieu; and keep this holy kiss" (4.1.41-43). Then he kisses her. True, there's no stage direction saying that he kisses her, but the line demands it, and his kiss (which must be agony to Juliet) puts an exclamation point on his blind self-assurance.
Exit Paris:
When Paris is out of earshot, Juliet's true emotions erupt. She says to Friar Laurence, "O shut the door! and when thou hast done so, / Come weep with me; past hope, past cure, past help!" (4.1.44-45). There's no actual door to shut, but imaginatively Juliet is now inside of Friar Laurence's cell, where she can pour her heart out. Sympathetically, Friar Laurence tells her that he has already heard that she must be married to Paris on Thursday and that there's no way to delay it. Juliet replies that she only wants to hear how the wedding can be prevented, and that "If, in thy wisdom, thou canst give no help, / Do thou but call my resolution wise, / And with this knife I'll help it presently" (4.1.52-54). She has a knife and her "resolution" is to kill herself. If Friar Laurence can't show her any other way out, all she wants from him is to tell her that killing herself is "wise."
Holding the knife in her hand, Juliet declares that God joined her heart to Romeo's, and before "this hand, by thee to Romeo seal'd, / Shall be the label [seal] to another deed [ i.e., marriage], / Or my true heart with treacherous revolt / Turn to another, this shall slay them both" (4.1.56-59). The Friar must give her good advice, and give it immediately, "or, behold, / 'Twixt my extremes and me this bloody knife / Shall play the umpire" (4.1.63). Juliet's "extremes" are her extreme difficulties, the ever-mounting pressures being put on her by her mother, father, nurse, and would-be husband to betray her love of Romeo. The knife is not actually "bloody," but she is determined that it will be, because it will decide the struggle ("play the umpire") between herself and those forces. And then she puts a terrific pressure of her own on Friar Laurence, saying, "Be not so long to speak; I long to die, / If what thou speak'st speak not of remedy" (4.1.66-67).
Juliet raises the knife as though to plunge it into her breast, but Friar Laurence stops her, saying, "Hold, daughter! I do spy a kind of hope, / Which craves as desperate an execution / As that is desperate which we would prevent" (4.1.68-70). Everything about the Friar's idea is desperate. Juliet's determination to kill herself is desperate and the Friar's plan is going to require desperate courage. Also, the Friar's plan is itself a desperate attempt to save Juliet's life. He says that if she has the strength of will to kill herself in order to avoid marriage with Paris, "Then is it likely thou wilt undertake / A thing like death to chide away this shame, / That copest with death himself to scape from it" (4.1.73-75). The phrase "That copest with death himself to scape from it" describes Juliet; she is willing to encounter death itself in order to escape the shame of marrying a second husband.
Juliet is indeed ready to "undertake / A thing like death," and more. She tells Friar Laurence that she can leap off a tower, become a thief, hide with serpents, be chained up with roaring bears, spend every night among dead men's bones, or lie beside a corpse in a new grave--anything, rather than marry Paris. "And," she adds, I will do it without fear or doubt, / To live an unstain'd wife to my sweet love" (4.1.87-88). Hearing this, Friar Laurence lays out his plan. She should put away the knife, go home, look cheerful, and say that she will marry Paris. Tomorrow night, Wednesday, she is to make sure that she sleeps alone, without the Nurse in the room. Then, says Friar Laurence, as he shows her a vial of liquid, "Take thou this vial, being then in bed, / And this distilling liquor drink thou off; / When presently through all thy veins shall run / A cold and drowsy humour" (4.1.93-96). A liquor that is "distilling" permeates the whole body as soon as it is drunk. This is why Juliet needs to be in bed; the fluid ("humour") will immediately ("presently') chill her into a coma. The Friar goes on to describe how her sleep will make her look dead--without color, eyes shut, stiff, cold--then promises, "And in this borrow'd likeness of shrunk death / Thou shalt continue two and forty hours, / And then awake as from a pleasant sleep" (4.1.104-106).
Friar Laurence then explains the rest of his plan. First, when the bridegroom comes to wake her (as the custom was) on Thursday morning, he will think--and so will everyone else--that she is dead. Then, by the common practice of Verona, she will be laid, uncovered and in her best clothes, on a bier and carried to the vault of the Capulets. "In the mean time, against [in preparation for the time when] thou shalt awake, / Shall Romeo by my letters know our drift [plan], / And hither shall he come: and he and I / Will watch thy waking" (4.1.113-116). "Watch thy waking" means that Friar and Romeo will keep watch over her until she wakes up; the Friar seems certain that both he and Romeo will be there in the vault well before Juliet awakes. When she does, Romeo will take her to Mantua. Friar Laurence concludes by questioning whether or not Juliet is strong enough to do what is required. He says, "And this shall free thee from this present shame; / If no inconstant toy [whim], nor womanish fear, / Abate thy valour in the acting it" (4.1.118-120).
Juliet accepts the challenge. She takes the vial from Friar Laurence and cries, "Give me, give me! O, tell not me of fear!"(4.1.121). At this, the Friar urges her to be strong and says he'll send another friar to Mantua with letters for Romeo. Taking leave of Friar Laurence, Juliet says, "Love give me strength! and strength shall help afford. / Farewell, dear father!" (4.1.125-126). She's asking love to give her strength and affirming that the strength that love gives will bring her ("afford") the help she needs to carry out her part of the Friar's plan. With this show of courage by Juliet, the scene ends.