Is he grateful to the servants for carrying out his orders? So with you: when you have carried out all your orders, you should say, "We are servants and deserve no credit; we have only done our duty" Luke 17:9, N.E.B.
More than once I have winced as I have read Jesus' statement as recorded in today's text. Perhaps you too have felt that it portrayed a heartless and ungrateful God. In the parable, the master makes his slave work hard all day, gives him not a word of thanks when he comes home sweaty and dusty, and--even worse--won't let him eat until he has fixed supper for the master, put on an apron, and served him. On top of it all, he then expects the fellow to say, "I'm just an unworthy good-for-nothing servant; I just do what I am told."
All of Jesus' parables are expected to tell us something about the Father. I suspect that if we had a videotape of Jesus telling this parable we would have seen a twinkle in His eye as He unfolded this parody of the master/servant relationship. By the tone of His voice we could have readily caught a touch of sarcasm, because Jesus was trying to expose the nonsense of people doing life's ordinary tasks for the sake of getting rewards from others.
The point is that God has unfolded to us patterns for living that have value in and of themselves. We live healthfully, for example, because it is wise to do so, not so that we can run to God with upturned palms expecting Him to give us some cherished treasure as a reward. While a child may regularly brush his teeth in order for Mother to say, "You're a good boy; I'll give you a new toy," it would be sadly immature for a grown man to expect trinkets from his dentist after every good checkup.
In the parable, Jesus described the ideal servants as ones who were at peace with the reason why they had done their daily activities. They were not seeking merit or reward, or trying by their works to curry special favors from their master.
No, our Father is not an ungrateful, authoritarian overlord. But neither does He use His gratitude to get us to do things that our own good judgment should command to us, lest we become fearful that we may not have worked hard enough to deserve supper!