For I know the plans I have for you,” declares the LORD, “plans to prosper you and not to harm you, plans to give you hope and a future.

God was about to send them into eighty years of captivity, because of what they did, but he gives them a promise, a hope, that they could grasp while they were in exile. He loved them so much, he warned them and pleaded for them to repent for 23 yrs. And now that they're going into exile, he gives them good advice and promises a future and a hope for them despite what they've done.