They are turned back to the iniquities of their forefathers - A great reformation had taken place under the reign of Josiah, and the public worship of idols had been abolished, and most of the high places destroyed; but under the reign of his son and his successors, they had turned back again to idolatry, and were become worse than ever. It required a captivity to cure them of this propensity: and God sent one: after that, there was no idolatry among the Jews.
Their forefathers - literally, “their fathers, the first ones:” in allusion to the idolatries committed in the wilderness, and by the generations whose history is given in the Book of Judges.
And they went after - Rather, yea! they have walked “after other gods to serve them.” The “they” refers to the men of Jeremiah‘s day.