Jesus used the Mustard Seed and Starter Dough parables to demonstrate that the Kingdom of Heaven is a living and active presence that is increasing within the realm of human experience.
Would you give a hungry child a poisonous arachnid to eat? Probably not, because even sinful human beings are not totally depraved. Would God give you something dangerous and destructive when you ask him for help? Certainly not, because he is the source and foundation of all goodness. In the Fathers Give Good Gifts simile, Jesus concludes his reassuring arguments that God can be trusted to provide for his full-time disciples when they pray the Lord’s Prayer.
Even casual Gospel observers notice that some of Jesus’ parables and similes come in pairs that resemble one another so strongly that they might be regarded as twins. But how does one determine which parables and similes truly are twins, and which might just bear a family resemblance? In this post David N. Bivin and Joshua N. Tilton suggest five criteria that authenticate parables and similes as true twins.