This pericope is composed of five distinct rhetorical elements:

• a pair of questions about an analogy for the kingdom of God;

• the parable of the mustard seed;

• the parable of the leaven;

• the narrator's summary;

• citation of Ps. 78:2.

None of the synoptic gospels records all of these. Matthew has the last four without the introductory rhetorical questions. Mark has the first two, followed directly by the narrator's summary, without the parable of the leaven. Luke has only the first three. The quotation from Ps 78 is found only in Matthew.

The parallels between the various synoptic versions of this material are extensive enough to make some sort of literary relationship probable. That makes the editorial seams in each evangelist's location of these verses all the more significant. 

Matthew provides the smoothest transition from the preceding material. For he introduces the parable of the mustard simply as "another" in a string of parables presented by Jesus as he taught a crowd along the shore of the sea of Galilee: the third straight parable invoking the image of a man sowing some kind of seed.  The fourth parable on Matthew's string, however, introduces a new simile: a woman using leaven to make bread.  Matthew then concludes this scene with sweeping generalizations that 

• Jesus said nothing in public without using parables &

• this fulfilled a "prophecy" about parables used to proclaim cosmic secrets (Ps 78:2).

Yet, surprisingly, this narrative summary does not end Matthew's reporting of parables of Jesus. Rather, he proceeds to present

• an explanation of the second parable (the weeds & wheat) presented to the crowds &

• three more parables (the buried treasure, pearl & net) for the kingdom of Heaven. 

Thus, there are two odd things about the narrative structure of this segment of Matthew:  

• the global summary concerning Jesus' general use of parables is located near the middle of the string of seven parables in Matt 13 rather than at the end; &

• the parable of the leaven is reported with the seed parables before this summary rather than after it with the other analogies for the kingdom of Heaven (treasure, pearl & net).

In Mark, the narrator's summary actually concludes this segment on Jesus' parables. For, unlike Matthew, Mark does not report any further parables in this context. Moreover, before this summary Mark presents only parables using the analogy of a man sowing seed. The absence of the parable of the leaven in Mark 4 makes his three parable cluster more thematically coherent than the parallel cluster in Matt 13.

Yet, Mark's transition between the second & third parables in this cluster is logically disjointed. For it is the third parable with the sower motif (the mustard seed) that Mark, unlike Matthew, prefaces with this pair of rhetorical questions:

• "How shall we compare the kingdom of God?" &

• "What parable shall we use for it?"

There is nothing strange about using such a rhetorical device to focus audience interest on a proposed simile. It is, rather, the location of these questions in the Markan narrative that is odd: 

• Mark has these questions introducing only the last of three parables about God's kingdom; &

• the question of an appropriate analogy is introduced right after a parable (the harvest) in which Jesus proposes the image of seed being sown as a simile for God's regime.

Unlike both Matthew & Mark, Luke records the parable of the mustard seed in a narrative context (Luke 13) far removed from his discussion of the parable of the sower & the rationale for Jesus' use of parables (Luke 8). 

• Like Mark (but not Matthew), Luke introduces this parable with a pair of rhetorical questions.

• Like Matthew (but not Mark), he pairs the mustard seed analogy for divine kingship with that of the leaven. 

• Yet, unlike both Matthew & Mark, Luke does not conclude this couplet with a sweeping statement about Jesus' general practice of using parables in his public speaking.

Thus, Luke's version of these parables has some features that resemble the parallels in both Matthew & Mark but is quite independent of the presentation of this material in either of the other gospels.

The odd thing about the Lukan presentation of the parables of the mustard seed & leaven is not the mere fact of Luke's deviation from the wording & narrative syntax of the other synoptics.  For Luke regularly demonstrates his freedom from the letter of other gospel texts. Rather, it is the narrative context in which Luke decided to insert this pair of parables that is strange. He appends these parables to a healing story in which Jesus rebukes the leader of a synagogue who challenged his cure of a crippled woman on the sabbath. Luke concludes that story with the sweeping statement that:

• all of Jesus' opponents were shamed &

• all the crowd rejoiced for all the "glorious things that were happening."

Luke then introduces the parable of the mustard as Jesus' direct response to these events ("He said therefore..."). There is, however, no catchword or thematic link between this parable & the narrative scene that precedes it. Nor is there any obvious logical relation between public reaction to a controversial miracle & the two parables that follow it (mustard & leaven). Thus, the grammatical connection that Luke makes between these pericopes involves a logical leap.  

Luke is the only synoptic author who reports the cure of this crippled woman. Moreover, from the viewpoint of either word association or story logic, the context in which Matthew & Mark present the parable of the mustard seed is far preferable to that chosen by Luke. So, Luke's reason for placing this pair of parables here rather than where the other synoptic authors locate it is a redactional mystery than cannot be solved by comparison of these texts alone.

Image

This analogy for God's kingdom focuses on the growth of a single seed into a mustard plant (Greek: σινάπις). There are several varieties of this herb (white, black, Indian).  But Jesus' exaggerated claim (in Matthew & Mark's versions of this parable) that the mustard granule is "the smallest of all seeds" makes it likely that the species envisioned here is Mediterranean black mustard (Latin: Brassica nigra), whose seed is a dark reddish brown sphere measuring little more than one centimeter in diameter. 

Botanically speaking, a mustard granule is not the smallest of all seeds in the world. But while it is large enough to be seen at some distance & even picked up between one's finger tips, it is virtually weightless &, therefore, could be used as a proverbial metaphor (like the English "featherweight") for something that was next to nothing. 

Although mustard is a weed that grows wild, it has been cultivated from ancient times for the pungent oil produced when its crushed seed is mixed with liquid for use as a condiment or a medicinal aid. Yet mustard is an annual plant that grows so fast that it is the type of seed that most farmers would not deliberately sow in their fields.  A single mustard plant may grow to about 4 meters (15 feet) high in just weeks & sprout many leafy branches that overshadow other slower growing plants. To minimize this characteristic, mustard cultivated for its seed has to be planted only in the drier summer months. 

Since this parable focuses on the natural shelter or shade provided by the plant's branches, however, it is more likely it was the wild variety that Jesus had in mind.  Before modern methods of screening cultivated seeds, small amounts of miniscule mustard seeds would inevitably be found among the seed of any other grain & thus sown along with the desired crop when farmers planted their fields in the spring. 

Jesus' parable focuses attention not on the farmer's act of cultivation but rather on the symbiosis of wild nature. For in the hot summer months of this relatively arid region, small birds inevitably find welcome shelter in whatever shade is available, even if it is just an overgrown weed like the mustard plant.

Permutations

The sheer novelty of Jesus' choice of a miniscule seed that automatically becomes a giant plant as an appropriate analogy for God's kingdom is probably the reason for the permutations of detail in the variant narrations of this parable in the gospels. Although all versions make the same general point, none is identical.  These differences in detail are of great significance for resolving the synoptic problem.

While the logical structure of each version of this parable is similar, the rhetorical elements vary in length, form and imagery.  

• Length. In Greek as in English Mark's recounting is the most wordy, Luke's the least; yet Luke's preface is longer than Matthew's:

Greek words	Matt	Mark	Luke
preface	5	14	13
analogy	45	43	27
total	50	57	40

• Form. While the Matthean preface is in the form of a statement, the Markan and Lukan prefaces are in the form of a pair of rhetorical questions (as noted above).

• Imagery. The most obvious difference between these versions, however, is the variation in the details that each narrator chose to describe the growth pattern of the mustard plant:

Image	Matt	Mark	Luke
seed	smallest	smallest	--
sown	in field	on ground	in garden
becomes	biggest shrub	biggest shrub	--
	tree	--	tree
produces	--	branches	--
birds nest	in branches	in shade	in branches

Note that Mark & Luke both share some details with Matthew but not with each other. Matthew & Mark agree (teal) in contrasting the size of the seed with that of the full-grown shrub (details not mentioned by Luke).  On the other hand, Luke agrees with Matthew (tan) in characterizing the mustard plant as a "tree" (δένδρον) & locating the birds in rather than under its branches (details not found in Mark). 

What makes this pattern of variation surprising is that Mark's description of the mustard plant is relatively realistic, while the descriptions in Matthew & Luke are not.  The image of a mustard tree with birds "camping out" (κατεσκηεῦσεν) in its branches is a surrealistic distortion of nature that only those who were not familiar with mustard plants could accept without seeking further clarification.

 Echo of scripture

The idea of "birds of the air" camping in the branches of a tree was drawn, not from observation of any mustard plant, but rather from descriptions of the giant cedars of Lebanon in Hebrew scripture. 

Psalm 104
16	The LORD's trees are watered in abundance,
	the cedars of Lebanon which he has planted.
17	The birds build their nest in them,
	the stork has her home in the fir trees.

As the giant redwoods of the ancient Near East, the cedars of Lebanon were noted for their size & durability. So the Judean prophet Ezekiel chose the cedar as an appropriate metaphor for envisioning God's restoration of Israel after the Babylonian exile.

Later Jewish apocalyptic imagination so magnified the tree as a metaphor of a great kingdom that Daniel described the reign of Nebuchadnezzar thus:

This tradition of describing a strong kingdom as a tree with birds nesting in its branches has clearly influenced the conclusion of Matthew & Luke's versions of the parable of the mustard. For this parable was formulated as an analogy appropriate for God's own kingdom.    

Like the parable of the mustard seed which precedes it, the parable of the leaven stresses the phenomenal growth of something that is initially small.  But the only verbal link between these parables is their use as analogies for the "kingdom of Heaven" (God). The descriptions of mustard & leaven are themselves totally unrelated.

Image

"Leaven" (Greek: ζύμη) is raw sour-dough: a mixture of flour with a moist fermenting agent produced by yeast organisms acting on the sugars in fruit or vegetable matter.  Before the modern development of stabilized dry yeast, a small amount of raw dough from each day's batch of bread was put aside to start the next day's batch.  The on-going fermentation process in the leaven produces both the carbon-dioxide that makes bread rise & alcohol that turns the dough sour.  

Left unbaked for a long period of time, however, leaven spoils.  The annual purging of all leaven from Jewish homes in preparation for Passover celebrations added to its negative connotations. This practice was well known.  So, the Jewish Christian apostle Paul could use leaven as a metaphor for corruption even in an argument designed for gentile Christians:

1 Corinthians 5
6	"Your boasting is not good.
	Do you not know that a little leaven leavens the whole lump?
7	Cleanse out the old leaven
	that you may be a new lump,
	as you really are unleavened.
	For Christ, our paschal lamb, has been sacrificed.
8	Let us, therefore, celebrate the festival,
	not with the old leaven,
	the leaven of malice and evil,
	but with the unleavened bread of sincerity and truth."

Therefore, a parable that likened God's kingdom to leaven was bound to startle any Jewish or early Christian audience.

The dramatic imagery of this parable is made even more striking by the amount of flour to which the housewife adds the leaven.  Three cups (¾ lb.) of flour is enough to make a loaf of bread large enough to feed ten or more adults.  The three "measures" (Greek: σάτα = Hebrew: seah) that the woman uses in this parable, however, amounts to half a bushel (almost 18 liters) or more than 30 pounds of flour.  That would be enough to make at least 40 large loaves or sufficient bread to feed at least 400 people.  

Needless to say, such exaggerated imagery in the parable of the leaven, like that at the climax of the parable of the sower (30 - 60 -100 times), was designed to leave the minds of 1st c. Mediterranean peasants with the distinct impression that there would be a super-abundant yield in due time rather than immediately.  Had the narrator intended to stress the speed with which leaven acts there would have been no need to mention the volume of flour.  

Like the parable of the mustard, therefore, the parable of the leaven stresses the contrast between a small beginning and a great result.  Neither the potential of the leaven to go bad nor the length of time it would take for so much flour to rise is at issue in the scene sketched by this parable.  Rather, the author chose the graphic images of leaven & mustard seed to illustrate God's kingdom because of the innate characteristic of these particular pieces of organic matter to spread dramatically & dominate all around them.

Echo of scripture?

On hearing the parable of the leaven, a person who was well versed in Jewish scripture might recall that, the story of the announcement of Isaac's birth mentions the same exaggerated amount of flour as this parable.   Abraham demonstrates that he is a generous host to the strangers who suddenly appeared at his tent by rushing to tell Sarah to prepare an abundance of food in these terms: "Make ready quickly three measures (seahs) of choice meal, knead it, and make cakes" (Gen 18:6).

Yet, as striking as the mention of such a large amount of flour is, it is important to note that the two words, "three measures," & the general image of a woman preparing to bake are the only details that would suggest a link between Jesus' parable of the leaven & the story heralding Isaac's birth. The narrator of the latter stresses the urgency & haste with which Abraham & Sarah act.  The narrator of the parable makes no explicit mention of time.  If Abraham had instructed Sarah to take leaven as well as three measures of flour, then some allusion to this story might have been intended by the author of the parable.  But, not only does Abraham not instruct Sarah to use leaven, his insistence that she quickly prepare food for unexpected visitors who are already on their threshold makes it highly unlikely that anyone familiar with this story would have imagined her introducing leaven to prepare this amount of dough. Leaven does not spread instantaneously.  And the guests arrived after noon "in the heat of the day" (Gen 18:1).  Even using a lot of leaven it would take much longer than the few hours left to prepare the evening meal, to bake leavened "cakes" from half a bushel of flour.

Since the central element in Jesus' analogy for God's kingdom -- the leaven -- is not drawn from the biblical story of Abraham any echo of that story created by the parable's allusion to the same amount of flour must be regarded as secondary & unintentional.  The coincidental mental link between these passages is created by fuzzy connections in the minds of readers with access to a biblical concordance rather than in images clearly invoked by the author of the parable.  Moreover, neither Matthew nor Luke provide any hint that the parable of the leaven was meant to be interpreted in terms of traditional biblical imagery.  So, any attempt to get some symbolic meaning from the "three measures" of flour or other details in this parable amounts to speculative allegorization by some later interpreter rather than the authors of these gospels, much less Jesus or his original audience.

Uniform Performances

For anyone interested in the synoptic problem, however, the most important features of the parable of leaven are the facts that:

• it is recorded by both Matthew & Luke but not Mark;

• it is appended directly to the parable of the mustard in both Matthew & Luke; &

• its wording is almost identical in Matthew & Luke

Obviously, any agreement in wording or setting between the Matthean & Lukan versions of this parable cannot be credited to the influence of Mark.  Moreover, the reason for appending the parable of the leaven to the parable of the mustard cannot be attributed to common graphic imagery as with the three parables about seeds (the sower, harvest & mustard).  For the parables of mustard & leaven have no common catchword other than the analogy to the "kingdom" that would lead two authors writing completely independently to recall the parables of mustard & leaven in the same sequence.  The gospel of Thomas shows that these parables could & did circulate separately.  So their juxtaposition in two canonical gospels indicates the influence of some common literary source.

That indication is strengthened by the fact that the bulk of the wording of this parable (from "leaven" to "all leavened") is almost identical in the Greek text of Matthew & Luke.  In fact, there is a greater verbatim agreement between these versions of the parable of the leaven (13 straight Greek words with only minor variation) than there is in the parable of the mustard or any other pericope in this sample synopsis.   The extent of this verbal parallelism is made all the more striking by the fact that the Lukan literary context for this pair of parables is totally unrelated to their literary context in Matthew.  Thus, the parable of the leaven offers a critical test of the adequacy of any synoptic source hypothesis.

Unlike the parables of the mustard & leaven, the narrator's conclusion to this segment presents no major surprises or problems for an interpreter on the synoptics. Yet there are significant variations.

• Matthew & Mark present a summary statement about Jesus' teaching in parables at almost the same point in their narratives.  Luke has no parallel.

• Matthew cites prophetic warrant for teaching in parables (Ps 78:2).  Mark & Luke do not.

• Mark claims Jesus gave his disciples private explanations of all his parables. Matthew & Luke do not.

These observations must be covered by any theory that a particular synoptic author redacted the work of one or both of the others.