The apostles said to the Lord,
Increase our faith!
Why did the apostles say this? We don't really know.
It doesn't seem to be connected with what Jesus had been saying previously. Instead Luke has a number of sayings here that seem to be connected only by the fact they are all about following Jesus as his disciples.
Certainly being a disciple of Jesus requires faith, and the apostles were discovering that. They must have been impressed by the assurance that Jesus had, by the way he spoke of God as Father with a conviction and an intimacy that they had not met before.
And understandably they wanted to have the same conviction and intimacy; they wanted to see things the way Jesus did and share his outlook. It is often said that 'faith is caught, not taught', and they must certainly have caught it from his assurance and conviction.
But they realised that their faith was still weak and fumbling. They had a long way to go before they could know the Father as he did, know his will and purposes. And so they said:
Lord, increase our faith!
Rather disconcertingly, Jesus does not answer their question, at least not directly. Instead, he seems to give a mild reproach:
If you had faith the size of a mustard seed ...
which is about as big as a pin head.
But he also gives encouragement:
...you could say to this mulberry tree, 'Be uprooted and planted in the sea, and it would obey you.'
It's not the quantity of faith, but the kind of faith, that matters. Even a tiny speck of a faith that is sincere and wholehearted, that totally trusts God, can achieve amazing things.
But why does he give this bizarre example of the mulberry tree, which has an extensive root system, and it would be difficult to uproot, let alone plant in deep water? And what would be the point anyway? To impress people by showing miraculous powers?
So it is not a saying which should be taken quite literally. Instead it is surely one of Jesus' typically Hebraic exaggerations to emphasise his point. He is saying that by faith you can do the difficult, the unexpected, the unlikely if this chimes in with God's purposes.
However, it's one thing to have faith, or at least to profess that one has faith; it's quite a different matter to live by faith. That is hard. For faith means that the centre of our life has to shift from ourselves to God. And that is hard for two reasons.
First, we are all deeply self-centred. We want our own way; we want to be served rather than to serve. That is what is implied by original sin. To live by faith often goes against the grain. Part of the problem is sorting out which desires are self-centred and which are God-centred.
Secondly, the realities of faith are not visible. The Letter to the Hebrews describes faith as
the assurance of things hoped for, the conviction of things not seen. (11:1)
Such things are, by definition, not yet in our possession. We are more at home with what we can see, feel and touch. But
No one has ever seen God. (John 1:18).
And though Jesus has made him known, we do not now see Jesus. It is by faith that we know him in Word and Sacrament, and hold on to what he said:
I am with you always, even to the end of the world. (Matthew 28:20)
This invisibility of the things of faith must always have been a difficulty, but it is difficult for us now in a 21st-century way.
For the most part, our western culture simply dismisses the possibility of non-visible reality. It is more disregarded than argued against. If there is even a sense of a gap that needs to be filled, it is assumed that mainline churches are not able to fill it.
We cannot help but be affected by this cultural atmosphere. It may tend to unsteady our own faith. It certainly makes it harder to speak about our faith to unbelievers.
But that is the world in which we live, the world in which God calls us to spread his good news. So we should make our own the apostles' prayer:
Lord, increase our faith!
And also the prayer of the man whose son was sick:
Lord, I believe; help my unbelief. (Mark 9: 24).