That works do not justify. 'Our Lord having exhorted His disciples to good works, now proceeds to rebuke the vainglory which so often accompanies them, showing that as a master is under no obligation to a slave who performs his appointed tasks, so neither is God to us. But since God is gracious, He treats those who are slaves, as if they were free hired labourers, and recompenses their labours with a reward, and receives their service which is strictly due, as if it were meritorious, and gives a requital out of all proportion to the toil. Thus the goodness of God is stronger than His justice' (Euthymius).
Related Commentaries of Luke 17:7
Luke 17:7-10
7 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?
8 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?
9 Doth he thank that servant because he did the things that were commanded him? I trow not.
10 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.