Verse 21 “It is like leaven, which a woman took and hid in three measures of meal, till the whole was leavened.”
Leaven is a type of sin and how it grows. When Jesus said that the kingdom of heaven is like leaven, he meant that in this present Church Age man’s culture and man’s wickedness will continue to grow. The Church will have less and less influence on the people of this age. Of course, we should continue to be a positive influence because we are the salt and light that the world needs, and we may do good for some.