In Jeremiah 21:1-10 the prophet is confronted by Zedekiah, king of Judah, whom Nebuchadnezzar had installed on the throne in place of Jehoiakin (Zedekiah's nephew). In verses 1-2 king Zedekiah sends ambassadors to Jeremiah, hoping to hear news that Yahweh would be faithful to His covenant with Israel and deliver Judah with the same kind of "wonderful deeds" He used to deliver Israel in times past. These "wondrous deeds" are the same "mighty powers" and "wonders" of Exodus 3:20, Deuteronomy 34:12, and Psa. 106:8 (LXX). Zedekiah thinks Yahweh's faithfulness is a one-way street of blessing, as though Yahweh would do whatever it took to protect the reputation of His own house (i.e. the Temple in Jerusalem). Zedekiah knows that Yahweh delivered His people out of Egypt, through the wilderness, and into the promised land to build His house, and now that His house has been established in Judah, surely He wouldn't allow His enemies to destroy it, would He?
In verses 3 - 10, Jeremiah responds to Zedekiah. There we find out that Yahweh does not plan on destroying His own house, let alone allowing its destruction from the hand of His enemies. Instead, Yahweh is determined to destroy Israel's temple by the hand of Israel's enemies. In chapter 29, during this same period recorded in chapter 21, Yahweh commissions Jeremiah to write a letter to the Jewish exiles in Babylon, telling them to build Yahweh's house there, in Babylon, and to reject any prophet who claims otherwise. The same message is found briefly in this chapter, too:
He who stays in this city shall die by the sword, by famine, and by pestilence, but he who goes out and surrenders to the Chaldeans who are besieging you shall live and shall have his life as a prize of war. (v. 9)
In 21:3-10, Yahweh does promise the destruction of Jerusalem by the Babylonians, but by that time Yahweh had left Jerusalem and built His house elsewhere; by that time Babylon was also Yahweh's vassal state, and Israel was Yahweh's enemy.
I Myself will fight against you with outstretched hand and strong arm, in anger and fury and in great wrath. And I will strike down the inhabitants of this city, both man and beast. They shall die of a great pestilence. (21:5-6)
Here Jeremiah mentions Yahweh's "strong arm" and "outstretched hand," which is a description of holy war that Yahweh wages against His enemies (Exod. 6, Deut. 4, 5, 7, 9, 11, 26). But this holy war is against Jerusalem and their idolatrous rulers. This holy war is Yahweh vs. Israel, and the great Exodus power is still in Yahweh's hand. In verses 8-10 Yahweh graciously offers Israel a choice of life or death much like that given by Moses before crossing the Jordan (Deut 30:11-12), and later in the book of Jeremiah we learn that Israel responded to that offer by accusing Jeremiah of two sins: first, of conspiring with the rulers of Babylon, and second, of undermining Yahweh's promise to dwell in the midst of Israel in his "house", the temple. For those in Israel who were actually paying attention to Jeremiah's preaching, Jeremiah is clearly not pro-Babylon; he is pro-Yahweh, and he knows that Yahweh is using Babylon to wage holy war against a greater threat to His Kingship: Judah.
This was good news for the people of Israel, among whom Yahweh was building His house. Just because Yahweh had set His face against Israel (v. 10), that did not mean He had abandoned His people entirely. He simply chose to build His house elsewhere, in Babylon. During that time in Babylon, the land of Israel would have it's promised rest (ch. 29). During that time Yahweh would remain faithful to His covenant. He would bring rest to His people and their land, and he would deliver them from His enemies. After that deliverance and rest their Jubilee would come.
There are many lessons which can be gleaned from this history. Perhaps the most important one is found by recognizing that Yahweh's faithfulness includes His covenant curses, not just blessings. Christians often presume that God's faithfulness to us is equivalent to Him blessing us, and that is not true. God's faithfulness includes discipline and punishment. An important distinction can be made between those two, also. Discipline is what God does as a Father to His children. Punishment is what God does as a holy Judge against His enemies, even those enemies in covenant with Him. Why do Christians presume that God will not punish them? Is it because they're in a covenant-relationship with Him? Why do professing Christians presume that they are always in a position of safety from God's judgment? Is it because Yahweh is thought of only as their Father? Do they really believe God ceased being the just Judge of all at the cross? Christians like Zedekiah are certainly able to conjure up a cheap view of God's grace in their minds. The same is true with their understanding of God's covenant loyalty. Like Zedekiah, it is often presumed that Yahweh will not destroy those who take refuge in His house. They think Yahweh still dwells among them, and that they haven't contributed to anything wicked, thus provoking His wrath; and if they have, the sacrifice of Christ becomes their excuse to still live wickedly sometimes. Like Zedekiah, some of us presume that our Christian community, our church, our households, are not in any danger because that's where Yahweh chose to build His house in the first place, just like He did with the temple in Jerusalem. But was the temple under Zedekiah's reign still Yahweh's house? And was Jerusalem still His holy city? Jeremiah's message seems to portray otherwise.
Yahweh did leave Israel with hope though. But that hope was not in the temple in Jerusalem. That hope was in Him, and He went with His people to Babylon. Surely the voice of Rachel's weeping would be heard in Ramah, where her children would be slain by sword, famine, and pestilence (Jer. 31:15). But Yahweh's good news to those who hoped in Him was different. A virgin Israel would trust in Him and return from Babylon (Jer. 31:21). Unlike Rachel, she would be told to keep her voice from weeping and her eyes from shedding tears, because there was a promised reward from her faithfulness in Babylon (31:16-17). There was hope for the future of virgin Israel, as long as she trusted in God's covenant faithfulness to bless those who bless Him and curse those who curse Him--as long as she lived as His peculiar treasure gathered from the holy warfare waged against His enemies.