Yeast is often used in the Bible as a picture of sin, because it so easily contaminates everything. But here, Jesus uses the little mould to represent the gospel. In the same way that yeast is ineffective if it stays away from the dough, so the gospel has no power unless it is mixed into the world. 30kg for flour is a large batch and Jesus wanted His hearers to imagine the energy expended in kneading the yeast into it. The woman would have worked very hard as she stretched and pounded the moist dough.

Many people in the West have got used to depersonalising the spiritual influences on our lives. They prefer to think in sci-fi terms about 'forces of good and evil'. Life is then a matter of human skill in manipulating those 'force fields'. But such ideas are wrong, completely wrong. The Bible talks about a personal God, and the person who opposes God is the devil.
 

Here are two parables with the same meaning. The disciples would have understood that Jesus was strongly emphasising His point. But what is it? It is all about the kingdom of God, (described here as the kingdom of heaven because heaven is the dwelling place of God). A kingdom is the land which belongs to the king, and where the citizens accept the king's authority. It is a great privilege and responsibility to belong to God's kingdom.
 

At the end a series of parables, Jesus asked His disciples if they understood. They said they had, but it is difficult to know to what extent. The first time people learn anything, its freshness catches their attention, and with an explanation (the disciples needed the Lord's interpretation of the parables) they have a new insight. However it is only when the teaching has to be used, that the deep significance dawns on them. That would happen after Jesus went back to heaven and the apostles were left to lead the churches.