This comparison would have been striking. For those who had been baptized by John after confessing their sins, in expectation of the coming kingdom, this image would seem to contradict their understanding, because, while they hoped for a kingdom that would overshadow everything, a mustard seed is lost in the soil of the field. Was the kingdom of heaven to be buried?
However, this was an image familiar to them: a tiny seed that yet outgrows all the garden plants. Though technically a shrub, it can be called a tree, since birds nest in its branches and find shelter.
Here in Matthew 13:31 the kingdom of heaven is now compared, rather shockingly, with something very small, a mustard seed of just one millimeter. This shocking comparison would have rhetorically served to grab the audience’s attention. For people who have allowed themselves to be baptized by John the Baptist in the expectation of the kingdom that is at hand and after confessing their sins, this image would seem totally at odds with their conceptual universe. Yet this only becomes worse in what follows. The kingdom they await will overshadow everything, but the mustard seed is lost in the soil of the field. For some this could have initially raised the startling question of whether the kingdom of heaven being buried?.1
Jesus here returns to images familiar to his audience. The mustard seed is indeed smaller than any seed they knew, yet once sown it outgrows all the garden plants. Though technically a shrub, it may rightly be called a tree, since birds nest in its branches and find shelter.2
31 He put another parable before them, saying, “The kingdom of heaven is like a grain of mustard seed that a man took and sowed in his field.