Leviticus 25:42

For they are my servants, which I brought forth out of the land of Egypt: they shall not be sold as bondmen.

They are His servants because He brought them out of Egypt, and therefore they are not to be sold as bondservants or treated as the property of men. This belongs among His provisions for Israel, in which the people are declared to belong to Him by redemption. He is the owner of the land and the Householder over the whole earth, and the people hold the land from Him as His tenants. The seventh-year sabbath of the land and the fiftieth-year jubilee teach this same ownership.

Those arrangements require liberality and the overcoming of stinginess, with practical duties owed to one another. That practical care is missionary work and is the gospel of the Old Testament. The land was to rest every seventh year with no cultivation, and whatever grew of itself was to be left free to the poor and the strangers and to the flocks and herds. The rest was to invigorate worn-out soil and to teach dependence on God. By special interposition He made the sixth year yield enough for three years, as a constant lesson that He cares for the poor and has made provision for them and will bless obedient people upon their lands.