Jeremiah 34:1
The word which came unto Jeremiah from the LORD, when Nebuchadnezzar king of Babylon, and all his army, and all the kingdoms of the earth of his dominion, and all the people, fought against Jerusalem, and against all the cities thereof, saying,
The word came to Jeremiah while Nebuchadnezzar king of Babylon, with all his army and all the kingdoms and peoples under his dominion, was fighting against Jerusalem and against all its towns. That setting places the message in the reign of Zedekiah. It belongs to the section of Jeremiah covering the history of the two years before Jerusalem fell.
The chapters are not arranged in chronological order, and in chronological order this chapter comes after Jeremiah 21 and before Jeremiah 37. The prophecies after chapter 20 are out of order because the manuscript rolls were gathered together into one book out of order, but the chapter itself makes its own time clear. It comes late in Jeremiah's work in Judah, and this displacement makes no change in its teaching.
The chapter is part of the account of Zedekiah's crisis, including the king's attempt to carry out the law of release for servants and the lesson that he needed to obey the prophetic message. It shows that owning slaves was a practice permitted among the Jews but was never pleasing to God and violated the moral law. The prophecy describes the desolation of the earth during the thousand years after the second advent, when all the wicked have been destroyed at Christ's coming and the righteous have been raised or changed to immortality and have ascended with their Lord to the eternal city to reign with Him in the judgment of the wicked.