Matthew 13 neatly collects many of the Lord’s kingdom parables in a single chapter, which is appropriate since Jesus taught seven of these on the same day, some by the sea to a large crowd, and others indoors to his disciples only. Among the parables he shared with the crowds (but did not explain to them) were two that were obviously intended to go together: the first compared the kingdom of heaven to a mustard seed that grew into a great tree, the second compared it to leaven that contaminated three measures of flour.
That must have left more than a few Jews scratching their heads. More than a few Christians are still scratching theirs over them.