"If you have faith as small as a mustard seed," Jesus says in the Gospel of Matthew, "nothing will be impossible for you." That sounds good, but does it work in a world where seeds are genetically altered by an impatient few and hard to come by for countless others? In a world where the gulf between the very rich and the profoundly poor is constantly growing, can a mustard-seed faith make any difference? And can such a little bit of faith be sustained...