Jamieson, Fausset and Brown on Jeremiah 28:6

6. Amen--Jeremiah prays for the people, though constrained to prophesy against them (1Ki 1:36). The event was the appointed test between contradictory predictions (De 18:21, 22). "Would that what you say were true!" I prefer the safety of my country even to my own estimation. The prophets had no pleasure in announcing God's judgment, but did so as a matter of stern duty, not thereby divesting themselves of their natural feelings of sorrow for their country's woe. Compare Ex 32:32; Ro 9:3, as instances of how God's servants, intent only on the glory of God and the salvation of the country, forgot self and uttered wishes in a state of feeling transported out of themselves. So Jeremiah wished not to diminish aught from the word of God, though as a Jew he uttered the wish for his people [Calvin].