Jesus compared the kingdom of heaven to leaven in these words: “The kingdom of heaven is like unto leaven, which a woman took, and hid in three measures of meal, till the whole was leavened.” (Matthew 13:33)
There seems to be at least two ways in which the kingdom of heaven works as leaven. First, it acts as leaven in its influence on the world. The world in which we now live is far different from what it would have been had the message of the kingdom not been proclaimed. Second, the kingdom of heaven acts as leaven in our individual lives. Just as the leaven in dough changes it, even so the message of the kingdom changes our lives.
Understanding this principle, there are two things we should be doing. First, we should take the message of the kingdom into our own heart and life – thereby letting it change us to be as God would have us to be. Second, we should be spreading the message of the kingdom wherever we can thereby causing the kingdom to grow and increase in the earth.