The leavening of yeast must have seemed to ancient men a profound mystery, and yet something on which they could always depend. Just so does the supernatural enter our natural life, working in the hiddenness, forcing the new life into every corner and making the dough expand.
If the dough were endowed with consciousness, it would not feel very comfortable while the yeast was working. Nor, as a rule, does our human nature feel very comfortable under the transforming action of God, steadily turning one kind of love into another kind of love--desire into charity, clutch into generosity, Eros into Agape.
Creation is change, and change is often painful and mysterious to us. Spiritual creation means a series of changes, which at last produce a Holiness, God's aim for us.