Faith isn't an act of intelligence, it's an act of imagination. Every time you give them a new metaphor, a mustard seed, a field, a garden, a vineyard, it's like pointing something out to a cat - the cat looks at your finger, not at what you're pointing at. They don't need to understand it, they only need to believe, and they do. They imagine the kingdom as they need it to be, they don't need to grasp it, it's there already, they can let it be. Imagination, not intellect.