Friar Lawrence is giving Juliet the potion to be in the dead like state that will stop the wedding so she can get away and get to Romeo. It is important because it sets everything at the end of the play in motion.
Juliet begs for forgiveness from her father and the wedding get pushed up to the very next day. It is important because with the wedding pushed up a day she takes the potion earlier.
She is going through all of the possibility in her head of what could happen when she takes this potion. It is important because she is finally thinking something through and being mature.
In this scene Capulet , lady Capulet, and the nurse are getting ready for the wedding and they are about to go wake Juliet for it. It is important because it is like the calm before the storm before they find Juliet dead.
This is the scene where the nurse finds Juliet dead and calls for everyone else to inform them of her death. It is important because the family believes that she is dead and the plan is working so far.
This is the scene where Friar Lawrence is telling them about how Juliet is in a better place and how they need to make haste on her funeral. It is important because the plan is going smooth and they suspect nothing so things so far are going good.