Earlier this week one of my clergy friends asked this question in relation to this week’s Gospel: “Why did Luke choose a mulberry tree instead of a mountain?” She was referring to the fact that in this week’s Gospel, Luke has Jesus responding to the apostles when they ask “Lord, increase our faith!” with “If you had faith the size of a mustard seed, you could say to this mulberry tree, ‘Be uprooted and planted in the sea,’ and it would obey you.” (Luke 17: 5,6) This saying appears in Matthew as Jesus’ response when the disciples ask him why they could not heal a boy who was epileptic. Jesus says to them: “Because of your little faith. For truly I tell you, if you have faith the size of a mustard seed, you will say to this mountain, ‘Move from here to there,’ and it will move; and nothing will be impossible for you.” (Matthew 17:20) In the passage from Matthew, Jesus’ teaching is clearer and directly connected to something the disciples did, which is typical of how Matthew presents Jesus, as a Rabbi giving object lessons. Luke is typically more open-ended about what it is that Jesus is trying to teach the disciples. These differences aside, it isn’t really clear why Luke would choose a different example of a difficult thing for Jesus to use to illustrate his point about faith.
As I reflected on this question, my thoughts naturally turned to the differences between Matthew and Luke, and to the differences between mountains and mulberry trees. I can’t say for certain, but I think there is something instructive in the choices the different Evangelists made. Aside from being more didactic, Matthew is concerned with connecting the ministry of Jesus with the legacy of Moses and the prophets of Israel. He quotes heavily from the Psalms, where God is regularly described as “a strong rock” and the miracles Jesus performs in his Gospel often have to do with demonstrating God’s power over the natural world. Mountains being mighty, and mountains being places where prophets like Moses encountered God, it makes sense that Matthew would portray the faith of a true follower of Jesus as being capable of moving mountains. The God of Moses threw the horses and chariots of Egypt into the sea. The God of Moses gave the law on stone tablets on the top of a mighty mountain. The God of Moses gave power that could split rocks open and produce water out of a desert environment. The God of Moses and the Psalms can cause “the mountains to skip like rams” (Psalm 114:6) and the faith of God’s people gives them access to that power. Matthew would connect the faith that the disciples needed to this kind of power. It is the power of the creator God who can remake the world, for whom nothing is impossible. And yet, moving a mountain from one place to the other is demonstrating the power of God in a way that we have seen before.
Luke focuses on a different aspect of God’s power. It’s the same creative power, but instead of working on the big, obvious things, it works on the roots underneath the ground, completely changing how the tree lives in the environment around it. It may be that Luke thought a strong tree like the Mulberry tree best reflected this kind of transformation. Luke’s Jesus does not point to the biggest, most immovable object, but to a tree that surprises in its strength. The strength of the mulberry tree is in its roots and in its vigorous growth. Many gardeners discourage planting the Mulberry near homes or sidewalks, because its roots are so strong that they can break up pavement and grow into the foundations of structures. The challenge the Mulberry tree represents is more than bulk. It is the kind of tree that would be very difficult to remove once growing in a place. The kind of transformation necessary to take a tree like that out and cause it to grow in the sea (not a logical place for growing trees) is a total transformation. Faith, for Luke, is the kind of thing that destabilizes the most stable system, making a creative change that is much more radical than moving a rock, even one so large as a mountain. The Mulberry tree that obeys this faithful person is going to become an entirely different plant. The tree that is so firmly rooted in the ground will be placed in a new environment and expected to grow and become “rooted” there. I think this may be what Luke wants us to hear about the nature of faith: that it both transforms us radically, and makes it possible for us to live in uncertain and difficult environments. Matthew wants to teach us that God is so strong and so faithful that with faith, we can do anything. Luke wants to teach us that faith gives us the strength to change things even as firmly rooted as a Mulberry tree, and to adapt to environments as shifting as the sea.