When Jeremiah is writing the prophetic book of his own name, he is doing so with one clear image in mind – the exile of God’s people by Babylon. God has just shown Jeremiah that Hebrew people are going to be taken by Babylon into exile and live there for seventy years. God does promise that after those 70 years (roughly a life time, similar to the way in which the 40 year wilderness wanderings cost the people of Israel a lifetime) the people will return. 
Here in chapter 31, Jeremiah is given a vision to tell the people of Israel about their return – their “reverse exile”. One of the striking images of this reverse exile is the inclusion of people who Babylon would likely not have brought along: “among them the blind and the lame, the pregnant woman and she who is in labor, together; a great company, they shall return here.” (Jeremiah 31) God’s inclusion of these people, and even His failure to mention any of the “important” people of Israel is telling. God cares to include the people who would otherwise not be included.
This doesn’t change the fact that the people who are returning are still weeping. There is sin to be confessed and repented of. Inclusion doesn’t keep us from discipline, it dares us to enter into it.
Since this is “Reformation Week” with “Reformation Day” being the 31st, it may be interesting to note that the Reformer-in-Chief, Martin Luther wrote a thesis called “On the Babylonian Captivity of the Church.” In this thesis, Luther accuses the Roman Catholic church of his day of holding the church hostage like the exiles of the Old Testament. It is clear that has Luther was writing this, he was praying for a day when he would see a “reverse exile” like that mentioned here in Jeremiah 31.
This started as an addition to “Living the Lectionary”, a resource of University Lutheran. You can find more about Living the Lectionary at http://universitylutheranchurch.org/category/living-the-lectionary/