Adam Clarke on Leviticus 25:42

For they are my servants - As God redeemed every Israelite out of Egyptian bondage, they were therefore to consider themselves as his property, and that consequently they should not alienate themselves from him. It was in being his servants, and devoted to his work, that both their religious and political service consisted. And although their political liberty might be lost, they knew that their spiritual liberty never could be forfeited except by an utter alienation from God. God therefore claims the same right to their persons which he does to their lands; See the note on Lev 25:23.