This part of chapter 18 comes when the Giver and Jonas are talking about what would happen if anything happened to Jonas and what happened when the previous giver, Rosemary, elected to be released. The Giver points towards the permanence of memories and how they cannot simply disappear with a Giver. If a Giver dies, those memories are set free in a way and are visited on all of the community:
"I think I mentioned to you once," the Giver reminded him, "that when she was gone, the memories came back to the people. If you were to be lost in the river, Jonas, your memories would not be lost with you. Memories are forever."
The Giver thus points towards the way memories are handled and dealt with in this community, and the dangers that would exist if a Giver, like Rosemary, should die without being able to transfer those memories on to a different Giver and therefore protect the community from those memories.