Read Mk. 4:30-32 (Mustard Seed). In Jesus: A Revolutionary Biography, Crossan (2009) quotes the Roman author, Pliny the Elder, who wrote about the mustard seed in his extensive Natural History. "Mustard...with its pungent taste and fiery effect is extremely beneficial for the health.
It grows entirely wild, though it is improved by being transplanted; but on the other hand when it has once been sown it is scarcely possible to get the place free of it, as the seed when it fall geminates at once."
What can you imagine Jesus is teaching about the kingdom of God with this parable?