Ambrose of Milan
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. Observe then that they who have rule among us, do not thank their subjects, when they perform their appointed service, but by kindness gaining the affections of their people, breed in them a greater eagerness to serve them. So likewise God requires from us that we should wait upon Him as His servants, but because He is merciful, and of great goodness, He promises reward to them that work, and the greatness of His loving-kindness far exceeds the labours of His servants.
Boast not thyself then that thou hast been a good servant. Thou hast done what thou oughtest to have done. The sun obeys, the moon submits herself, the angels are subject; let us not then seek praise from ourselves. Therefore He adds in conclusion, So likewise ye, when ye have done all good things, say, We are unprofitable servants, we have done that which it was our duty to do.