The reason that Juliet comes to see Friar Lawrence is that she does not know what to do. Her parents are going to force her to marry Paris, but she is in love with Romeo and she has already married him. So she can't marry Paris, and she can't tell her parents what she has done...
I think he agrees to help her for a few reasons:
- He married her to Romeo and knows she can't marry Paris.
- He does not want her to commit suicide because Catholic teaching says you can't go to Heaven if you kill yourself.
- He does want her to stay alive so that her marriage to Romeo can help to heal the feud between their two families.
At this point, Juliet's parents have become very frustrated with her because she doesn't want to marry Paris and it may seem to them that she doesn't have a very good reason not to marry. This is a bit of dramatic irony because we as audience members know exactly why she doesn't want to marry him. The nurse even recommended that this would be a good choice since Romeo is banished.
Juliet wants a solution to this problem of feeling forced to marry Paris. Since Friar helped them in the past, I believe she thinks he will do it again.
Every time I read this scene, I am led to believe the Friar does this for one of three reasons:
1. He believes in true love. This would seem out of character for a friar, but maybe he was a big sucker.
2. He is covering his own action that he could feel guilt about: marrying Romeo and Juliet in the first place.
3. He truly believes that what he stated about Romeo and Juliet's marriage bringing the families together. He hopes to see a stop to their feud if only the news can be broken at the right time.