Luke 17:1-10
1 Jesus said to his disciples: “Things that cause people to stumble are bound to come, but woe to anyone through whom they come. 2 It would be better for them to be thrown into the sea with a millstone tied around their neck than to cause one of these little ones to stumble. 3 So watch yourselves.
“If your brother or sister sins against you, rebuke them; and if they repent, forgive them. 4 Even if they sin against you seven times in a day and seven times come back to you saying ‘I repent,’ you must forgive them.”
5 The apostles said to the Lord, “Increase our faith!”
6 He replied, “If you have faith as small as a mustard seed, you can say to this mulberry tree, ‘Be uprooted and planted in the sea,’ and it will obey you.
7 “Suppose one of you has a servant plowing or looking after the sheep. Will he say to the servant when he comes in from the field, ‘Come along now and sit down to eat’? 8 Won’t he rather say, ‘Prepare my supper, get yourself ready and wait on me while I eat and drink; after that you may eat and drink’? 9 Will he thank the servant because he did what he was told to do? 10 So you also, when you have done everything you were told to do, should say, ‘We are unworthy servants; we have only done our duty.’”
Can You Muster Mustard-Seed-Size Faith?
Do you know how big a mustard seed is? Microsoft’s Copilot tells me it’s “approximately 1 to 2 millimeters.” You would need 100 to 150 mustard seeds lined up to make an inch. We’re talking tiny.
Do you know what’s smaller than a mustard seed? My faith. At least, that’s how I felt after Sunday School one Spring Day some 30 odd years ago. We were reading this Gospel text from Luke 17 and my Sunday School teacher was explaining the line, “If you have faith as small as a mustard seed, you can say to this mulberry tree, ‘Be uprooted and planted in the sea,’ and it will obey you.”[1] My teacher asked us, “If you could do anything in the world – think of the craziest thing – what would it be? If you have strong enough faith, you can do it.”
I would guess that I was somewhere between 8-12 years old at the time. So, when my Sunday School teacher asked me what I’d do if I could do anything in the world, the first thing I thought was, “I’d fly!” So, I tried.
Thankfully, it wasn’t from the roof of my house. I just closed my eyes, and prayed really hard, “Lord, let me fly.” I clenched my fists and pushed off the ground, and… nothing. And do you know what I thought next? “I don’t have strong enough faith. My faith must be even smaller than a mustard seed. I’m not a very good Christian.”
Fast forward to 2025, confronted with the same Bible passage, I feel eerily similar, but for a slightly different reason. Jesus just told us a parable about what a servant should say after a hard day of work: “So you also, when you have done everything you were told to do, should say, ‘We are unworthy servants; we have only done our duty.’”[2]
I get the first part; I’m certainly unworthy. That’s not hard to admit. But I’m not sure I could say the second part, i.e. that I’ve only done my duty. Could you? Have you – done your duty?
Jesus just laid out what a Christian’s duty is. There are two things Christians are supposed to do when it comes to sin – prevent it and address it.
Jesus said to his disciples: “Things that cause people to stumble are bound to come, but woe to anyone through whom they come. It would be better for them to be thrown into the sea with a millstone tied around their neck than to cause one of these little ones to stumble.”[3] You have a duty, i.e. a sacred responsibility to do everything within your power not to cause anyone else to sin. But we lay that snare in each other’s lives so very often.
It can start with a word. And then, all of a sudden, what could have been – should have been – a constructive conversation between two Christians erupts into a shouting match full of finger pointing and unfair or outright false accusations. One person oversteps; the other overreacts. The more it’s punctured and bruised, the more pride swells on both sides. That’s what Jesus is talking about. Hurt feelings are bound to happen in life, but woe to that Christian who brings the hurt, intentionally or otherwise.
It can start with a look. You thought it was going to be a chill night in front of the TV, but your entertainment selection proved to be more salacious than you anticipated. You just wanted to look nice, e.g. try out the new outfit that’s been burning a hole in your closet. You didn’t know the thoughts it would spur (or maybe you did and didn’t care), and before you know it, you’ve caused more than one heart to burn with lust. Again, lust is bound to happen – especially in the world we live in – but woe to that Christian who causes it.
And this is important! Jesus says that it would be better for you to have a millstone tied around your neck and for you to be thrown into the heart of the sea than to make your fellow Christian angry. And that’s not hyperbole. Jesus is dead serious, because sin is deadly serious, which is why he also expects us to address it.
“If your brother or sister sins against you, rebuke them; and if they repent, forgive them. Even if they sin against you seven times in a day and seven times come back to you saying, ‘I repent,’ you must forgive them.”[4]
If a fellow Christian sins against you, it’s your duty to confront them – and not in anger either, not playing the victim or martyr, but as he says so often elsewhere in Scripture: with great patience and careful instruction,[5] with gentleness and respect,[6] being completely humble and gentle, bearing with one another in love.[7]
Does that sound like how you respond when someone sins against you? Do you calmly and gently approach them about it? Or do you angrily approach other people and talk behind their back? Do you wash your hands of them and want nothing more to do with them? That’s not a Christian’s duty. It’s the opposite of what God wants from you.
Or when – by some miracle – you do address sin in a brother or sister, and – by some other miracle – they do repent, do you always forgive? Or do you indulge your guilt trip complex and lord it over them? Do you hold onto grudges and refuse to let go?
It's little wonder the disciples responded the way they did: “Increase our faith!”[8] It’s the same way I felt in Sunday School so many years ago. It’s the same way I feel today when I think about how often and how badly I fail to do my duty as a Christian. It’s the necessary response in a Christian’s heart, and the reason Jesus speaks these words to us – so that we don’t deny our wrongdoing; so that we don’t develop a self-righteous spirit; so that we don’t put confidence in ourselves but learn to rest it in him.
That was my problem in Sunday School. I thought that if my faith were strong enough – if I was strong enough in my faith – then I could do anything, even fly. But that’s not what faith is. Faith isn’t a muscle you flex. It’s reminder of how small you are, but how big your God is.
“Suppose one of you has a servant plowing or looking after the sheep. Will he say to the servant when he comes in from the field, ‘Come along now and sit down to eat’? Won’t he rather say, ‘Prepare my supper, get yourself ready and wait on me while I eat and drink; after that you may eat and drink’?”[9]
That’s the way the world works. That’s not the way your God works. What did Jesus do on the night before he died? While his disciples reclined to eat the Passover meal, Jesus was the one who got himself ready to wait on them. He took off his outer clothes, wrapped himself in a towel and washed their feet. Peter said it was inappropriate. Jesus reminded him that this was why he had come. As he had said elsewhere: “For even the Son of Man did not come to be served, but to serve, and to give his life as a ransom for many.”[10]
That’s what Jesus came to do for you. He came to serve you. He came to give his life for you on the cross as the sacrifice for your sin – to take your penalty in his body and die the death that you deserve so that you can live in the peace of knowing his selfless, forgiving love. A love that wasn’t limited to a one-time gift, 2,000 years ago on a hill outside of Jerusalem, but one that he continues to show you today.
Because Jesus does these other things too. He rebukes you when you sin. Which doesn’t sound pleasant at first. He points out your faults and failures, but not to humiliate you, not to run you down, but to make you aware of your error, so that you can see how he has made it right, so that you can understand your need for forgiveness and salvation, and find it in Jesus.
Jesus does what’s so hard for you and I to do. He forgives everyone who sins against him. He forgives you. And he does it in ways that are intentionally hard for you to deny. He has a pastor pour water on your head and pronounce God’s adoption and blessing over you. He has a pastor and a vicar and lay leaders within the congregation, put his own body and blood into your hands so that you can taste his forgiving love with your own lips. He puts fellow Christians in your life to serve as his mouthpiece and proclaim his promise of salvation to sinners like you – people who don’t deserve his love but receive it by grace through faith in Jesus.
That’s what I had gotten wrong in Sunday School so many years ago. I thought I had to be the strong one. I thought that moving mulberry trees was up to me and my ability. Faith is a complete denial of self. It’s an acceptance that we are smaller-than-a-mustard-seed-Christians, who put their faith in a God who is great, who does the impossible for us – who sent his Son in love to forgive us, to wash our sins away, and to give us new opportunities every day, not to earn his love but to live in it, to see the world as he does.
That’s the only way you will ever be able to avoid causing someone else to sin, when you see them the way that Jesus does – as souls dearly bought by his own blood. Then we’d do anything, including sacrificing our own comforts and privileges and rights, if it means serving someone else’s eternal, spiritual good.
That’s the only way we can ever rebuke someone else’s sin, without sitting on our own high horse, when we see ourselves the way that Jesus does – as sinners saved by grace. Who better, then, to be the ones to tell other sinners where they can find grace too? That’s why God forgives you – because he loves you and wants to live with you forever in heaven, but also so that you can forgive each other too.
That’s the only way we can ever say, “We have only done our duty,” when we acknowledge how humble our service is to the God who gives us Jesus. We are unworthy. The other way to say that is, he is gracious. Lord, increase our faith that we may serve you by loving each other. Amen.
[1] Luke 17:6
[2] Luke 17:10
[3] Luke 17:1,2
[4] Luke 17:3,4
[5] 2 Timothy 4:2
[6] 1 Peter 3:15
[7] Ephesians 4:2
[8] Luke 17:5
[9] Luke 17:7,8
[10] Mark 10:45