But which of you, having a servant plowing or feeding cattle, will say unto him by and by, when he is come from the field, Go and sit down to meat? And will not rather say unto him, Make ready wherewith I may sup, and gird thyself, and serve me, till I have eaten and drunken; and afterward thou shalt eat and drink? Doth he thank that servant because he did the things that were commanded him? I trow not. So likewise ye, when ye shall have done all those things which are commanded you, say, We are unprofitable servants: we have done that which was our duty to do.
Boucher, M. I. (1981). The Parables. Wilmington, DE: Michael Glazier, 1981 ISBN 9780894531309
Ancient Slavery as an Interpretive Context for the New Testament Servant Parables by Mary Ann Beavis Journal of Biblical Literature, Vol. 111, No. 1 (Spring, 1992), pp. 37–54