Theophylact of Ohrid
Catena Aurea · Lukasevangelium 17
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.
Because faith makes its possessor a keeper of God’s commandments, and adorns him with wonderful works; it would seem from thence that a man might thereby fall into the sin of pride. Our Lord therefore forewarned His Apostles by a fit example, not to boast themselves in their virtues, saying, But which of you having a servant plowing, &c.