A little leaven leavens the whole lump.
I suppose we are most of us rather surprised that "leaven" is generally used in a bad sense in Holy Scripture. Not, indeed, always; because the kingdom of heaven itself is likened to leaven; but generally. In the New Testament leaven is mentioned on five distinct occasions, and on four of these as a type of something very evil, as a symbol of a thoroughly mischievous activity. In the Old Testament, the prohibition of leaven in all the offerings made to God occurs to us at once. It must, however, be allowed that this prohibition has two distinct origins, the one of which (and the earlier and most important) is purely historical, and carries with it no notion of good or evil. The total avoidance of leaven during the annual solemnity of the Passover, although it afterwards acquired a moral significance, was simply ordained in memory of their hasty flight from Egypt (Exodus 12.). The other prohibition, however, is of a moral and typical character: the exclusion of leaven from the sacrifices of God distinctly gave a moral character and meaning to its absence (Leviticus 2:11) Now let us ask what leaven is, and whether there is anything in its own nature to explain the evil significance which Holy Scripture has attached to it. Leaven, then, is simply so much dough in a state of fermentation. When the last "lump" had been leavened, and was ready for baking, a portion was set aside to act as leaven for the next "lump." Now the process of fermentation is one of the most curious, and (until lately) most obscure among the commoner operations of nature. It is now known to be due to the rapid — often inconceivably rapid — development of vegetable (fungoid) growth, which has the power of disengaging a quantity of free acid, and of changing the chemical character of the substance on which it acts. It is believed that most, if not all, contagious diseases are due to fermentation imported into the blood; and the terrible danger of these diseases is only a striking proof of the extreme facility with which fermentation spreads. This is, indeed, its one great characteristic — a characteristic which governs at once many of the most ordinary and useful operations of life, and many of its most deadly and widespread evils. Fermentation may, indeed, be conveyed by one substance into another, as in the common case of dough "raised" by means of yeast. But the ordinary and typical method is that of leaven, which is itself fermented dough, introduced into the midst of other unfermented dough. The invariable consequence is, that the fermented portion has the power of superinducing its own chemical condition upon the mass with which it is placed in contact: being itself in a state of violent chemical change, it has the power of setting on the same change all around it; nor will this action cease until that of which it is a part has entirely succumbed to its influence. But this change is, in its entirety, a change for the worst: it may, indeed, be checked (as in bread by baking, in wine by adding spirit, or by other means); but unless stopped at an early stage it is hurtful; and when it cannot be checked, as in decaying substances and in fatal diseases, it is simply destructive. Thus fermentation does, as it were, spring from evil and end in evil; it originates in that which is corrupt and hastening towards dissolution, and it ever tends to reproduce the same. Only when carefully watched, and mastered, and held in check, does it lend itself to real usefulness. And even so it retains some reminder of its evil origin. Yeast may be tasteless and harmless enough; but leaven is fermented, i.e., "sour," dough, and always imparts a certain sourness to the bread which is made with it. It is in the nature of all complex organic substances to be subject to a destructive fermentation; they are only kept from it, only preserve their delicate chemical balance, by the principle of life (whatever it may be) within them The very law of leaven and its power stands in the fact of like to like; and even so false teaching can only act with rapidity and certainty when it comes to minds disposed to receive it — when it jumps, i.e., with the popular errors and exaggerations of the day. But with moral evil it is different, because that evil is always in us more or less, and therefore the leaven always finds something apt to work on if it be admitted. There is in most of us, at any rate, a large body of imaginations which are ready to swell, to work, to become turbid, to disengage a quantity of evil temper and evil feeling, and to ruin the proper sweetness and savour of our Christianity, if once we have opened our hearts to the contagion of malice and wickedness. In 1 Corinthians
5. St. Paul passes, by an easy transition, from the natural to the historical associations of leaven. As sedulously as all ferment was banished from the houses of the Israelites, so sedulously should the moral ferment be banished from the hearts of Christians.
(R. Winterbotham, B. Sc.)
Parallel VersesKJV: A little leaven leaveneth the whole lump.