John Calvin Commentary Jeremiah 3:10

"And yet for all this her treacherous sister Judah hath not returned unto me with her whole heart, but feignedly, saith Jehovah." — Jeremiah 3:10 (ASV)

He continues with the same subject: that the Jews were not moved by any fear when they saw the dreadful vengeance executed on their fellow countrymen because of their sins. Her perfidious sister, he says, did not return to me, that is, after so many warnings by the prophets and such an example of punishment. However, he adds an explanation: she did not turn with her whole heart, but feignedly and falsely.

The Prophet here anticipates objections the Jews might have raised: “What! You deny that we have returned! Is not the whole land cleansed from idolatries? Is not God worshipped according to the requirements of the law? Is an altar still seen under the shade of trees or on hills?” Since they might have evaded the charge in this way, as they usually did, the Prophet counters such an evasion and says, “Though they have, in appearance, given some tokens of repentance, yet they have only put on a disguise and have acted falsely towards God, for there is no integrity in them.”

We now see more clearly why he had previously specifically mentioned the time of Josiah, for the Jews then returned feignedly to God. In the king and in a few there was a right feeling, but in the rest, there was only dissimulation. God then, in a few words, shows that he does not care for reformation that is false and feigned, but that he requires a genuine feeling within; hence he thus concludes: