Luke 13:21

“It is like to leaven, which a woman took and hid in three measures of meal, until it was all leavened.”

But He has another purpose in the second illustration and that is to introduce women into the equation. So He selects as His second example a woman's occupation, bread-making. The woman puts a little leaven in the flour and soon it spreads throughout the whole. In the same way, so should women (and all) spread the Good News of the Kingly Rule of God from one to another until it has reached all.

Leaven is a piece of dough kept back from the previous batch which has fermented. It is put within the new dough and ferments the whole, until the whole is affected. And here the thought is that it is used because it results in a better product. It is an apt picture of the God's word. It is introduced from outside and commences its work once it is received, and goes on until the whole is affected. It stands here too as a warning. Do not think that you can receive but a little of Christ. Once Christ is allowed in He will not cease His work until the whole is transformed.

‘Three measures of meal.' A standard measurement signifying sufficient for the task in hand.