Jesus is finishing the picture He began in Luke 17:7. No master tells a servant just in from the field to sit down and eat first. He says, Make my supper, get ready, serve me, and then you can eat. The question expects everyone to agree: of course that is what a master would say. Barnes says the parable seems to have been spoken "with reference to the rewards which the disciples were expecting in the kingdom of the Messiah." He suggests they may have been impatient for those rewards, and Jesus was showing them that service comes first and reward comes at the master's time. Gill reads it as a word given "to keep the disciples humble in the performance of such miraculous works," since Jesus had just spoken of faith that could uproot a tree (Luke 17:6).

No one needs to answer; every listener knew how a master spoke to his servant. Jesus presses the point with a second question, "Doth he thank that servant because he did the things that were commanded him? I trow not" (Luke 17:9). Then He turns it on the apostles: "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" (Luke 17:10).

In the parable the servant works in the field and then must still wait on his master at supper. Barnes says the words "by and by" in Luke 17:7 "should have been translated 'immediately.'" The master would not have the servant eat as the first thing: "Hungry and weary he might be, yet it would be proper for him first to attend upon his master."

The Greek question opens with ouchi, a strong form of "not" used in questions. "Gird thyself" translates perizosamenos, "having girded yourself about." Gill notes a Jewish rule that a master "is obliged to make them equal to himself" in food and drink in the case of a Hebrew servant. On Luke 17:7 he adds that the disciples had no such servants, since they had left all to follow Christ: "Christ only puts this for instance, and supposes such a case."

This question is about how servants of God should think of themselves, not about how God treats His servants. The apostles had asked for more faith (Luke 17:5). Jesus answers that even great faith does not make the servant the master. Barnes puts the lesson this way: we have "conferred no favor" on God, and "If he rewards us, it will be matter of unmerited favor."

The same Gospel shows the other side. When Barnes explains "gird thyself," he points to Luke 12:37, where the returning lord "shall gird himself, and make them to sit down to meat, and will come forth and serve them." No earthly master in Luke 17:8 would do that, yet in Luke 12:37 Jesus pictures a lord who does exactly that for his watching servants. The servant does not earn the table, but the Master may still choose to set it.