John Gill's Exposition of the Whole Bible
Jeremiah 34:9
That every man should let his manservant, and every man his maidservant, [being] an Hebrew, or an Hebrewess, go free,.... This is the proclamation that was agreed to be made, that every manservant and maidservant, that serve six years an apprenticeship, should be freed from their servitude, according to the law in Exodus 21:1; a law founded upon justice and equity, mercy and compassion; done for the honour of the Jewish nation, that they might be a free people, and in commemoration of their deliverance from their servitude in Egypt. This law, as it seems, had been long neglected, and servants had been retained in bondage beyond their due time, through the oppression and covetousness of their masters, and the neglect of the civil magistrates; who should have took care that such a law was put in execution, and that servants were not oppressed. Some have thought that it was at the beginning of the sabbatical year that this proclamation was made, when, according to the law, there should be a release of servants, Deuteronomy 15:1; but that was not a release of servants, but of debts; for if a servant had not served out his time, the sabbatical year, or year of release, did not discharge him; though the year of jubilee did, according to Maimonides l, who says,
"if the year of release happens in any of the six years, he (the servant) serves in it; but if the year of jubilee happens within the time, even though he has been sold but one year before it, he is free;''
that none should serve himself of them, [to wit], of a Jew his brother; or cause them to serve him, oblige them against their will to continue in his service; or by any means avail himself of them, and receive to himself any profit or advantage by their service, they being Jews and brethren; which seems to be added, both as the reason of the law, because they were brethren of the same nation and religion with them, and to distinguish them from other servants, who notwithstanding this law might be retained as such.
l Hilchot Abadim, c. 2. sect. 2.