Jesus said to them: Because of your unbelief. For, amen I say to you, if you have faith as a grain of mustard seed, you shall say to this mountain, Remove from hence hither, and it shall remove; and nothing shall be impossible to you.
Origen
Or, all faith is likened to a grain of mustard-seed, because faith is looked on with contempt by men, and shews as something poor and mean; but when a seed of this kind lights upon a good heart as its soil, it becomes a great tree. The weakness of this lunatic’s faith is yet so great, and Christ is so strong to heal him amidst all his evils, that He likens it to a mountain which cannot be cast out but by the whole faith of him who desires to heal afflictions of this sort.
Imported from an open dataset — not yet checked against the printed edition.