Luke 17:5-10 finds the apostles being mentioned for the first time since Luke 9:10. Luke has been intermingling stories about Jesus with the larger group of disciples as well as the Pharisees. The
apostles have the good sense to know by now that they need to turn directly to Jesus regarding this question faith. They also know that the Pharisees are always registering dissatisfaction with Jesus practices and teaching (Luke 15:1-2; 16:14 ff).
The issue of faith has arisen a few times in Luke to this point (Luke 5:20; 7:9, 50; 8:25, 48). It is a little
surprising that it is so infrequently front and center. It leads us to ask, “What does Luke mean by faith?”
And how is the master-slave analogy work with the mustard seed? Luke does use this analogy for
instruction on faith, relationships, and status (Luke12:35–48; 16:1–9; cf. 22:24–27).
So the apostles are requesting that Jesus bestow (in some sense) faith upon them. It is as though faith is a quantitative commodity. If you get enough of it you are all set. Discussions abound among interpreters
about the mustard seed in Luke and also in Mathew 17:20b. Is Jesus using it to rebuke the apostles for so little faith or encouraging them to use their small faith. I think Jesus response to them using the mustard seed combined with the gigantic mulberry tree suggests that a little faith can provide extraordinary things and the apostles are required to only use what they have.
The danger is that the apostles seem to think that they can accumulate faith like you can accumulate money or possessions. Faith is a qualitative matter. The opposite of faith is not doubt. As the theologian Paul Tillich reminded us faith is courage. When you see faith it looks like courage. Faith is courage to do the right thing. Faith will not remove fear and trembling. Faith will not guarantee victory or the abolishment of disappointment.
The next part of our reading is the master-slave set of questions. The first part is directed to the master (Luke 17:7-9). All the questions expect a resounding “No” as the answer.
The “thanks” spoken about in Luke 17:9 is easily misunderstood by a contemporary reader. In antiquity the “thanks” referred to here is not the verbal expression of gratitude. It means a kind of reward such that the master would be indebted to the slave for having done what the slave was required to do. A slave who does what they are supposed to do places no obligation on the master.
In the second part (Luke 17:10) the slave is directly addressed. And we arrive at the “so what” of the master-slave saying. Here the so called “worthless slave” is the one who does that which is required and no more. “Worthless” does not mean useless. It means the slaves to whom nothing is owed. It is the slave who completes what is required and no more.
At least two implications from these loosely connected sayings of Jesus spoken to the apostles will need elaboration as one reflects further. 1) All that is required of those who follow Jesus is to courageously give what they have been given. Faith is a qualitative matter. 2) As one faithfully serves they are warned not to think that mere obedience will result in reward or being more highly treasured. Go back and read Luke 17:1-4 that begins these sayings of Jesus and remember the 24/7/365 responsibility of discipleship.