This scene is when Friar Lawrence is trying to tell Paris that he should not marry Juliet. This is important, because Friar is trying make sure that there's no rush to this and prevent anything bad from happening.
The scene where Juliet is begging Friar Lawrence for forgiveness is important, because in this scene Friar Lawrence is really planning a way for Juliet to be with Romeo which is to fake her own death.
The scene when Juliet is about to take the potion for her to fake her death is important, because everything is about to go downhill, after she takes the potion. She's really thinking about this too.
The scene where Juliet is lying to her father, Capulet, saying that she will marry Paris and that her father changed the plans of the wedding from Thursday to Wednesday is important, because her father is actually proud of her and if they change the wedding plans it can change the whole plan of Juliet faking her death.
This scene when Nurse and her parents find out that Juliet is "dead" is important , because now that means that the plan is starting to work and it's now starting to get sad. Because Juliet is gone. (Not really)