In Shakespeare's Romeo and Juliet, what are the reasons that lead Friar Lawrence to give Juliet the vial of potion?

After being informed that her father has agreed to give her in marriage to Count Paris, Juliet is desperate. She is, of course, already married to the banished Romeo. In the beginning of Act IV, she goes to Friar Laurence to seek advice. She threatens to kill herself if the Friar does not have a solution. The Friar comes up with a plan which will help Juliet avoid marrying Paris. Earlier in the play, he...

After being informed that her father has agreed to give her in marriage to Count Paris, Juliet is desperate. She is, of course, already married to the banished Romeo. In the beginning of Act IV, she goes to Friar Laurence to seek advice. She threatens to kill herself if the Friar does not have a solution. The Friar comes up with a plan which will help Juliet avoid marrying Paris. Earlier in the play, he married Juliet to Romeo, so he cannot marry her again. He also wants Romeo and Juliet to be happy, so the only solution seems to be to reunite the two young lovers. The audience also knows that the Friar is somewhat of a scientist (he speaks of this in Act II, Scene 3) and so it is plausible that he could come up with a plan for Juliet to fake her death.

It involves Juliet taking a potion which will make her seem as though she is dead for almost two days ("two and forty hours"). His plot has three important parts. First, Juliet must put on a happy face and tell her father that she will agree to marry Count Paris. Second, she must actually drink the vial of potion while she is alone in her bedroom. He tells her that it will cause her to become "stiff and stark and cold" and that the rosiness of her lips and cheeks will "fade." Third, the Friar plans on sending a letter to Romeo to inform him of the plan. He will instruct Romeo to come to Capulet's tomb where Juliet will be placed, and to be there at the time when the girl is set to wake up. Romeo will then take her with him back to Mantua and they will be "free" from "shame." Juliet, who demonstrates a fearless and courageous nature, agrees to the Friar's plan and goes off with the vial.