John Calvin on Jeremiah 29:28

The crime ascribed to Jeremiah was, — that he rendered the captives indifferent, so that they cast off every hope of deliverance, and disregarded their own country. But the design of Jeremiah was far different; it was, that the people might not by too much haste anticipate the promises of God, and that he might also extend their hope to the end, prefixed. As there are two causal particles here found, כי על-כן, ki ol-ken, some give this rendering, “For for this cause,” that is, because he claimed the name of a Prophet. The simpler meaning however is, that he gives a reason why Shemaiah blamed the neglect of the priest, even because he (Jeremiah) had habituated the captives to bear their exiles. But he reproached the holy man, as though he had made them indifferent through long delay. Jeremiah had indeed said that the time would be long; but this particular phrase, It is long, means a different thing, as though Jeremiah wished to bury in oblivion the hope of a return, because it would have been foolish to languish so long.