And He [Jesus] said, “How shall we picture the kingdom of God, or by what parable shall we present it? It is like a mustard seed, which, when sown upon the soil, though it is smaller than all the seeds that are upon the soil, yet when it is sown, it grows up and becomes larger than all the garden plants and forms large branches; so that the birds of the air can nest under its shade.” Mark 4: 30-32.
The Creator, saying that the mustard seed was the smallest of all seeds, knew that the mustard seed wasn’t the smallest of seeds. Critics who embrace the literal reading of the Bible know this too. So they use Jesus’ statement, thinking it a mistake, as proof that He couldn’t be God.
What the critics fail to consider, or don’t want to, is that the Bible is inspired literature that’s presented in different forms. In this particular case, Jesus’ statement was in the form of a parable. If it were meant to be taken literally, it would mean that the kingdom began in the shape of a mustard seed. Instead, Jesus was simply conveying the sense that the kingdom, like a mustard seed, began small.
The reason that He used the mustard seed as an example is because it was a regular, typical measurement-comparison in the minds of the people spoken to; it being the smallest seed familiar to the region. In fact, research shows Jewish texts commonly citing the mustard seed to represent insignificance and humility. One such example is by a Jewish philosopher named Nahmanides (13th century AD). He wrote about the universe expanding, saying that at its conception it was like the size of a mustard seed.
Parables shouldn’t be literally read. Jesus used them as allegorical illustrations, analogies or statements to teach spiritual truths, principles, and moral lessons.