Throughout the history of the Church some congregations have celebrated this meal with leavened bread and others with unleavened bread. We are not told explicitly in the NT which sort of bread God requires and therefore we believe that Christians are free to choose. We know that leaven can represent malice and envy (1 Cor. 5:8), but Jesus also says that the kingdom of God is like leaven which works through the entire loaf (Lk. 13:21). So which is it? The answer of course is, yes. Leaven means growth and maturity, but growth and maturity is not an automatic blessing nor is it neutral. The question is always what is growing? Is it cancer or a tumor? Then it needs to be cut out. Is it good muscle and strong bones? Then we can rejoice in it. And sometimes leaven needs to be got rid of not because of any inherent evil but because you’re growing up. Children give up pacifiers and diapers. Older children don’t hold their parents hands when crossing the street. Young adults leave their parents and marry and begin families of their own. And parents let their older children go into the world. These are good and healthy transitions if they are done with thanksgiving and obedience to God.
We use leaven in our communion bread perhaps for many reasons, but one of them is because we want to emphasize the growth of the kingdom, the promise of the gospel. The gospel is not merely clinging to old things or wishing we could get back to some better time. The promise of the gospel always takes us forward. In this meal you are eating mature bread, fermented bread and mature wine, fermented grape juice. This is the life of the kingdom, and the kingdom is not done. It’s growing. And it will grow until it fills the whole earth. Some come, eat and drink, and trust that God knows what he’s doing. He’s growing us up; so trust him.