What day is “so great” and “a time of distress for Jacob,” and how will he be saved from it?

In a cry of lament (Alas!) the coming destruction is described as That day. This picks up on the Day of the Lord which is a common theme in the prophets.  Jeremiah refers specifically to the Day of the Lord in Jeremiah 46:10, but on other occasions, as here, speaks of that day or in those days (see further Jeremiah 31:31–34;Jeremiah 33:14). The Day of the Lord does not refer to any one specific date or event but is rather a period of indefinite time in the Lord’s unfolding plan of redemption. It is a period that includes judgment at different times, all of which point forward to the final day of judgment. In this passage the judgment event referred to is the time of distress  for Jacob. The name Jacob is used here to describe the nation of Israel in their lowliness and is referring to Judah which is all that is left of Israel at this point.¹ The great judgment that is coming is the Babylonian invasion. 

The message of the Book of Consolation, however, is that the imminent, unavoidable and destructive judgment that is coming to Judah will not be the end of Israels’ story, as the final phrase of Jeremiah’s vision indicates:  Yet he shall be saved out of it. The Lord is not done with Israel; he will save his people. The Lord will act powerfully to completely transform the distressing situation they find themselves in. The Day of the Lord is not just a time of judgment, but, as the following passages will clearly show, it is ultimately a time of salvation and redemption. It is in fact a time of salvation and redemption through judgment.