Leviticus 25:55
For unto me the children of Israel are servants; they are my servants whom I brought forth out of the land of Egypt: I am the LORD your God. For unto me the children of Israel are servants; they are my servants whom I brought forth out of the land of Egypt: I am the LORD your God.
Israel are God's servants because He brought them out of the land of Egypt. That ownership was put into practice in the land laws, in which the Lord is owner and householder and provider of the land while the people hold their place in it as His tenants. Every seventh year cultivation was to cease and the land was to rest.
What grew of itself in that resting year was to be freely available to the poor and to strangers and to livestock. The sabbatical year and the jubilee in this way taught liberality. The yearly sabbath allowed the soil to recover and taught dependence on God's provision, so that the rest of the land and its produce reminded Israel of His care and His claim over it.