"yeast leavens a whole loaf"?

In a recent Jesus Radicals discussion, someone replied to me saying,
Doesn't Jesus' teachings on the Kingdom of God describe something that starts small and becomes pervasive and systematic? Yeast leavens a whole loaf. Seed that populates a field of fertile soil. Financial investments that make returns. A crop that grows and gets harvested. Do we do a disservice to the concreteness of the Kingdom if we, a priori, reject the possibility of pervasive and systematic manifestations?

... I find [the author's] desire for reconciliation between powerful and powerless to be spot on. The Lion shall lay down with the Lamb.

I replied:
You seem to be drawing quite broad conclusions from what looks like a rather cursory reading of those parables. Yes, yeast spreads through the whole loaf, but that doesn't mean the whole loaf is yeast. The yeast (like the kingdom) remains a small portion, just distributed throughout. Yes, the seed (of the sower) brings a generous return, but only a fraction of the seed fell on fertile soil, while much of the seed fell on rocks, or was eaten by birds, or was choked by weeds. Again, the kingdom is amazing where it exists, but it still remains a fraction (or minority) amidst the world.

And this understanding fits with the other things Jesus said, that those who find the way of life are few, and about his followers being persecuted (which doesn't happen when they are the majority, in power, controlling the social systems). It also fits with Jesus' example of avoiding the powers of the crowds and the systems of control. Yes, his kingdom is real and concrete, as Jesus was. And it's also small and vulnerable, as Jesus was.

"The lion shall lay with the lamb" is of course escatalogical prophecy (Is 11). Many other escatological promises speak of the rich and powerful being brought down and judged, not somehow reconciled. And then it is to be fulfilled by God, not by our own systemic manipulations, shifting the power we can muster over to God's service.

When we think we're achieving "pervasive and systematic manifestations" of the kingdom of God (perhaps also West's "massive examples"), those successes are more likely failures, our efforts being assimilated for purposes quite far from Christ's. As Jacques Ellul put it:
...These successes, this efficacy as it would be called from man's standpoint, and especially in our own society, will never amount to anything more than the approval given by the world, by society, to certain acts and means. It is the stamp of a group of men, a social body. But if we do not believe that society is good and right, this approval proves nothing except that the action is in conformity with the world. It does not mean that the world has changed; quite the contrary. Each time the people of God becomes effective according to the world's criteria, this only implies that society has absorbed our action and is using it for its own ends and for its own profit. ...The efficacy we think we have is simply a power in the world's service, for the perfecting of its own being, for its better organization....

I think church history has supported his interpretation of this process...