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?
Note 4 at Lu 17:7: This parable is part of Jesus' response to His disciples' request in Lu 17:5 to increase their faith. As mentioned in note 3 at that verse, Jesus basically replied that they had faith, but they weren't using it. This parable illustrates this point.
Servants would not expect to reap their benefits with only a partial day's work. They must fulfill all of their duties before they can expect their pay. That's their reasonable (Ro 12:1) duty (Lu 17:10). Likewise, if we would be more concerned about using faith to serve our master (i.e., God) than serving ourselves, then He would see to it that our needs are met (Mt 6:33 and Lu 17:8). We do have sufficient faith (see note 3 at Lu 17:5), but we must get out of a self-serving attitude (Jas 4:3) and use our faith to serve others (Mt 25:40).