Charles Ellicott Commentary Luke 17:6

"And the Lord said, If ye had faith as a grain of mustard seed, ye would say unto this sycamine tree, Be thou rooted up, and be thou planted in the sea; and it would obey you." — Luke 17:6 (ASV)

If you had faith as a grain of mustard seed.—These words remind us, and must have reminded the disciples, of those in Matthew 17:20, which were called forth by the disciples' failure to heal the demoniac boy after the Transfiguration.

The “sycamine tree” takes the place of “this mountain,” namely Hermon, as an illustration of what true faith could do. This tree is probably not the same as the “sycamore”; it is identified by most botanists with the mulberry tree. The mulberry tree is still cultivated on the slopes of Lebanon and in the neighbourhood of Jerusalem and Nablus, both for its fruit and as food for silkworms.

If we suppose the conversation to have taken place near the Sea of Galilee, both features of the comparison gain a local vividness. It is remarkable that our Lord meets the prayer with what sounds like a reproof; and such a reproof, we must believe, was needed. The most elementary faith would have been enough to teach them (assuming the connection traced above) that God is love, and that He would help them to overcome all hindrances to their love being patterned after His own. There was something, it may be, false in the ring of that prayer, an unreal diffidence asking for that as a gift which really comes only through active obedience and the experience gained through it.