Jamieson, Fausset and Brown on Jeremiah 30:5

5. We have heard ... trembling--God introduces the Jews speaking that which they will be reduced to at last in spite of their stubbornness. Threat and promise are combined: the former briefly; namely, the misery of the Jews in the Babylonian captivity down to their "trembling" and "fear" arising from the approach of the Medo-Persian army of Cyrus against Babylon; the promise is more fully dwelt on; namely, their "trembling" will issue in a deliverance as speedy as is the transition from a woman's labor pangs to her joy at giving birth to a child (Jr 30:6).