The parable of the Mustard Seed is not about ambition or success. It teaches that small should not be ignored. We should note that Jesus uses a mustard seed as a metaphor for the reign of God. It grows to become bushes, serving birds and people who need them. He would have used a cedar tree, a symbol of glory and success, for the reign of God. But he chooses a tiny seed of mustard to show that marginalized persons have the potential to realize.