Because: Matthew 17:17, Matthew 14:30-31; Hebrews 3:19
faith: That is, as Bp. Pearce well remarks, a thriving and increasing faith, like a grain of mustard seed, which, from being the least of seeds, becomes the greatest of all herbs.
a grain: Matthew 13:31; Mark 4:31
nothing: Mark 9:23; Luke 1:37, Luke 18:27