52 loaves of bread (3 measures of flour) is what you can make from just 12 TBSP of yeast (leaven). This parable illustrates how just a little yeast can explode into a massive amount of bread that could feed hundreds of people.
The amount of yeast to flour is so small, you would not even know the yeast was there, as to hide, so to speak. This is an addition to the parable of the mustard seed discussed yesterday that even a small amount of the word can change lives and spread about the kingdom.
Another way I realized you could think of this parable is that there are 52 weeks in a year such as the amount of loaves. Just a small amount of the word (yeast) every week can have dramatic spiritual benefits in your life as it begins to grow in your own life and spill into the lives of the ones around you.