The Giver explained why the people needed a Receiver of Memory. What were the reasons? What is his role in the community?

In Ch. 13, the Giver explains some of the reasons why the community needs a Receiver of Memory.

We know that the community went to Sameness many generations back and that caused the Elders to decide that having memories burdened individuals too much. So, they began to deposit these memories in a Receiver of Memories so they could access them when needed, but otherwise did not have to bother with the emotional toll they can...

In Ch. 13, the Giver explains some of the reasons why the community needs a Receiver of Memory.

We know that the community went to Sameness many generations back and that caused the Elders to decide that having memories burdened individuals too much. So, they began to deposit these memories in a Receiver of Memories so they could access them when needed, but otherwise did not have to bother with the emotional toll they can take. We don't know much about the world when individuals had their own memories, but the Giver does describe ten years prior when the previous Receiver of Memory left. 

"It was chaos." he said. "They really suffered for a while. Finally it subsided as the memories were assimilated. But it certainly made them aware of how they need a Receiver to contain all that pain. And knowledge."

Individuals in the community really have no memories of the previous generations because they simply don't need them. They are always told what to do and when to do it, and any major decisions in their own lives are made by the Elders. The Elders themselves don't even have these memories, thus the Receiver of Memory is required, almost like a safe, to hold all of these collective memories for reference.

His role in the community is to advise the Elders whenever they need it. But this doesn't happen often. 

"Only when they are faced with something they have not experienced before."

Like the plane flying into their airspace at the beginning of the novel. They wanted to shoot it down, but the Giver advised against it because he knew it could bring on a war. They didn't understand the larger consequence of shooting down a plane because they had never been to war.