What happened to the memories Rosemary was given when she was granted her wish of release? How has
this event help shape the rules for future Receivers of
Memory?

When the previous receiver in training (The Giver's daughter Rosemary) failed in her training, her memories were released back into the community.  She could not give them back to the Giver, and in the book's world, the memories don't just die with her.

Instead, the memories dispersed (it seems like they just went up in the air and people got them in their brains) and were felt by all the people.  This was really bad because all of a sudden all the people of the community had to feel things and remember things that they were totally not ready for.

Explanation:

in that passage i would say the sentence which best describes the overall impact of the setting is when they mention the absence of people because it suggests that taking a walk at night is unusual.

to inform the reader that the text will take a second look at the grimms’ original tales