Matt 13: 33, Luke 13: 20-21
He told them another parable. “The kingdom of heaven is like leaven which a woman took and hid in three measures of meal, till it was all leavened.”
Completely Non-Expert Interpretation:
To put in terms a non-homemade bread baking society might better understand, the leaven is like soaping a fountain. It takes just a little bit to put on a big, bubbly show!
In the bible, leaven (yeast) is sometimes symbolic of evil in the world but in this parable, the leaven is positive. It represents the grace of God lifting up the world through the church. Each Christian is supposed to be out and about being the leaven you want to see in the world.
Three measures was about 50 pounds of meal and would have been enough to feed over a hundred people which, here, symbolize the world. Even though the small amount of leaven is hidden, it is actively working its way through and raising a very large amount of dough.
Just as, compared to the fountain, the amount of soap may be small and (due to the fact that the offending party dumped it into the fountain in the middle of the night under the cloak of darkness so they wouldn’t get arrested for vandalism) fairly undetectable, but, before anyone knows it, it’s making a big impact because it is a miniature Mount Everest made out of suds in the middle of a park.
To recap: though persecuted or blown off as an archaic, outdated, unneeded institution from a less enlightened time, the Church lifts up the culture, undetected, with its Jesus teachings on human dignity, worth and rights, love of neighbor, forgiveness, caring for the marginalized, etc. even though many in the culture have no idea where these concepts originated from.