Progressive reflections on the lectionary #84

Monday 29th September 2025

Luke 17:5-10 Reject magical thinking and behave more like a mustard seed, your loyalty will lead you to do what you ought to do

The lectionary offers us another very familiar passage from Luke’s gospel this week - perhaps familiar because of it’s strangeness. Faith is compared to a mustard seed - but perhaps not in the way that everyone seems to think - and then there’s a bit of problematic chat about enslaved people and their treatment. In this reflection I will mainly focus on the faith like a mustard seed thing offering an alternative approach to the standard view of what Jesus is saying here before very briefly explaining how that relates to the last few verses.

The lectionary gospel passage this week skips straight to the second half of a conversation. Luke has set this up by instigating a typical piece of conversation about ‘little ones’ - which we can read as ‘the vulnerable’ - who are Luke’s great concern.

“It would be better for you if a millstone were hung around your neck and you were thrown into the sea than for you to cause one of these little ones to sin,” says Luke’s Jesus in forthright terms.

It is this no-nonsense one liner, and some follow up about the importance of repentance and then forgiveness, that prompts the disciples to respond, perhaps rather desperately: “Increase our faith!”

And that’s how we end up at the mustard seed thing - about which I’ve heard approximately a billion sermons, reflections etc. I’ve been given mustard seeds to hold, I’ve seen pictures of mustard plants, you name it - I’ve heard it/seen it. All of those reflections, though, have tended to revolve around the idea that it is the size of the seed that matters. “Faith the size of a mustard seed…” And to be fair that is what we get in a lot of translations, not all though.

The thing is that this all relies on the approach we take to what Jesus was doing - our view of what he was trying to achieve. Contemporary Christianity relies a lot on the idea that Jesus was trying to change people’s beliefs - and I concur with that to some extent - but only to some extent. Because ultimately I think Jesus was more interested in behaviour - and only in belief in so far as it related to behaviour.

I am going to do two things. First I’m going to talk about ‘faith’, then I will talk about the mustard seed idea. Reframing our understanding of these two ideas gives an alternative perspective on this short interaction. Then finally I’ll quickly link it to the final verses.

Although we can tend to consider it a ‘religious’ or ‘spiritual’ idea, the word ‘pistis’, which we translate as ‘faith’, had a meaning in the first century that was as much political as anything.

Pistis/faith denoted the key (personal and communal) characteristic of loyalty, and the quality of being trustworthy. It’s a relational idea that is expressed though action.

Although in religious terms it is now generally used to relate to ‘believing’ in particular teachings, it was actually much more about being in a trusting relationship. It’s a response of shared loyalty to a person or cause rather than an intellectual or emotional attachment to a private, or individual, belief system.

That’s why we sometimes see pistis translated as ‘faithfulness’ (e.g. Galatians 5:22) - because it’s a character trait, not a doctrinal stance.

The writer we call Luke, who wrote both his gospel and the book of Acts, uses pistis a lot in relation to stories of healing, inclusion, and crucially: reversal. In his writing it is faith and/or faithfulness (loyalty/trust) that turns things upside down.

Now, if we read these texts through a lens of magical thinking then we are naturally led in one direction when it comes to thinking about faith - we are led to expect the inexplicable/impossible on the basis of believing hard enough. This gives rise to plentiful theological problems, not least the difficulty of the inconsistent triad (if God is all powerful and all good, then how come bad things happen) and the reality that if it (faith = believing hard enough) works, its very much on a part-time basis.

If, though, we read Luke’s writing about faith differently, focussing instead on action based on trust and loyalty - then we get a different result. If the marginalised are restored because of people being loyal to, or trusting in and acting upon, Jesus’ ethic of radical welcome then we get a different result. In other words, if we behave like a new world is here - then we start to get a new world.

How, then, does this relate to mustard seeds?

The key thing to grasp here is that the Greek word used in this verse (six) is not, actually, to do with size.

The literal translation is “if you have faith like/as (hōs) a grain of mustard” - some translators, though, have taken it upon themselves to see hōs, which elsewhere is translated as ‘like’ or ‘as’, as relating to the physical appearance (size) of the seed.

They turn it into something that says something along the lines of: “if your faith looks like a teeny tiny little mustard seed,” rather than “if your faith behaves in the way that a mustard seed behaves….” Translation is interpretation, after all.

Depending on how we read this, it has the capacity to turn faith back into a sort of magic power. Just a spoon full, just a drop, of Getafix’ magic potion is enough to give you superhuman strength… just a mustard seed’s worth of ‘faith’ would mean you can do the impossible.

There is, however, an alternative way of looking at this, which is to say that if faith is ‘like’, or ‘as’ a grain of mustard then it has a similar sense of purpose. It is not so much to do with the amount of faith (trust/loyalty) you have - as what you have faith in (to what you are faithful/loyal) - what your purpose is.

If you know what you are - if you understand your purpose - then these difficult things, the repenting, the forgiving, the protecting of the ‘little ones’, become, if not easy, then at least part and parcel of who and what you are.

A mustard seed, after all, grows into a mustard plant - that’s all it can do. It can’t become a pine tree, or a courgette plant. It can only become a mustard plant. It might not be easy, but it gets on with it. The mustard seed doesn’t worry about the fact that it is small, and the plant is big - it just germinates and grows, and grows for the course of its life. The task is huge, but it has a singular purpose. If our faith (trust/loyalty) has a purpose like a mustard seed has purpose, then we can achieve these things (the caring, the repenting, the forgiving) because they are the natural outcome of our loyalty.

“If your loyalty to your purpose was like the mustard seed’s loyalty to its purpose,” says Jesus in this story, “you would act accordingly.”

The passage ends with the difficult stuff about slavery - I don’t have time, now, to do it justice, but look at the last line: “…when you have done all that you were ordered to do, say, ‘We are worthless slaves; we have done only what we ought to have done!’”

‘We have only done what we ought to have done’ - in our obedience to the principles of forgiving, repenting, and caring for the vulnerable - we have done only what we ought to have done.

If our commitment to, our loyalty to, our trust in our purpose is like that of a mustard seed, then we will get on with it and do the work. We will care for the vulnerable, we will repent, we will forgive.

Ultimately then, when we have cared for the vulnerable, when we have forgiven the repentant, when we have turned away from our own problematic behaviour and commitments, then we will simply say: “we are like mustard seeds after all, we have only done what we ought to have done.”

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