Why does the Giver refuse to leave the community?

In Lois Lowry's The Giver, Jonas makes the choice to leave his community. This decision will send the community into chaos, because all of the memories he is holding will be released to those that have never had to bear any of the feelings connected with these memories. The decision to leave the community is encouraged by the man training Jonas, who is known in the community as the Giver. Jonas has built a deep connection with the Giver and begs him to leave as well, but the Giver refuses. In chapter 20, the Giver provides two specific reasons that he will not leave.
First, the Giver knows that Jonas's departure will be incredibly difficult for the community to bear. The memories and feelings that will be released to the members of the community will be so unfamiliar and overwhelming that they will cause a great deal of upheaval. The Giver believes that the community can endure this, and be wiser for it, but they will need help and guidance in order for the transition to be successful. While the Giver believes it is time for the people to have their memories back, he is also concerned for them. He cares about the community and hopes to protect them and aid them through this difficult time. He knows that if he leaves with Jonas, it is likely that the community will not survive.
The Giver has also been weakened over the course of the year in which he has been transferring memories to Jonas. He knows that physically, he will be unable to make the difficult journey that lays ahead for Jonas. The Giver is keenly aware that it is likely that the transition in the community will be one of his final acts, and he accepts this fate with a lighter heart, because he believes that when he is through, he will die and be reunited with his daughter again. This belief sustains him and allows him to stand firm in his decision to stay with the community when Jonas leaves.