Jeremiah 29:16-19 are a digression that stresses the fact that the Lord would complete the judgment of Judah before any restoration would begin. [source][source][source]
The true message from Yahweh concerning the Davidic king, Zedekiah, and the remaining Judahites who were still in the Promised Land was that they would experience war, famine, and plagues. They would be like rotten figs: good for nothing (cf. Jeremiah 24:2-3). [source][source][source]