Jeremiah 34:14
At the end of seven years let ye go every man his brother an Hebrew, which hath been sold unto thee; and when he hath served thee six years, thou shalt let him go free from thee: but your fathers hearkened not unto me, neither inclined their ear.
The command was that at the end of seven years every man was to let his Hebrew brother go free, when a Hebrew sold to him had served six years, and the charge was that the fathers did not hearken and did not incline the ear to this command. The sale was a voluntary agreement for a period of service, paid for in advance, with the proceeds going to the servant or his family or toward his debts, and keeping the servant beyond the agreed term turned the service into involuntary servitude. The verse belongs to events in Zedekiah's reign, within the history of the two years before Jerusalem fell, as an indictment of the Jews for oppressing and enslaving laborers before its destruction by Nebuchadnezzar.
In the book the verse stands in Jeremiah 22-39 where the prophecies are not placed in chronological order, with chapter 34 coming late in Jeremiah's work in Judah, after chapter 21 and before chapter 37, its chapter itself making its timing clear, and this displacement makes no change in its teaching. Zedekiah did right by proclaiming liberty and undertaking to carry out the scripture concerning the jubilee, including the release of servants and other oppressed people, evidently intending to observe the Jubilee, which had not been done since the time of Moses. But he failed to carry it out, and withholding the promised freedom polluted the Lord's name.
The surrounding passage shows a covenant of liberty made by a sacrifice prepared by separating its pieces, with the covenanting parties passing between the pieces. This connects the sacrifice in Genesis 15 with God's covenant of freedom from sin through Christ. The year of release is a pattern that teaches God's people would be delivered from bondage after seven prophetic years, reckoned as 2,520 years from the captivity associated with Manasseh in 677 B.C. and ending in A.D. 1843.
Permitting people to own slaves was never pleasing to God and violated His moral law. Enslavement violated God's law, failure to release Hebrew servants was a serious national wrong, and Israel's disobedience to this law securing freedom at regular intervals was part of its adoption of slavery. That disobedience God condemned and punished and made a cause for His judgment carried out through Nebuchadnezzar's destruction and captivity.