The Mustard Seed: "A Kingdom for the Unclean and Disorderly"
Unlike most parables in the gospels, the Mustard Seed (Mk 4:30-32/Mt 13:31-32/Lk 13:18-19/Thom 20) is an actual metaphor for the kingdom of God. Jesus likens the kingdom to a mustard shrub to which birds flock and make nests in the shade of its branches, mocking, in effect, the cedar of Lebanon (Ezek 17:22-24, 31:5-6; Dan 4:10-12; Ps 104:10-17). What do we make of a mustard shrub that has pretensions to such grandeur? Before answering this we need to address discrepancies regarding (1) where the mustard seed is planted and (2) what it grows into.
Where is the seed planted?
There's no agreement where the mustard seed is planted. In Mark it is "on the land"; Matthew "in a field"; Luke "in a garden"; and Thomas "on tilled soil". Mark and Luke have claims to earliest tradition on this point. Brandon Scott prefers the latter, since the planting of mustard seed in a garden was forbidden in Jewish Palestine (Mishnah Kilayim 3:2), pointing to subversive originality (Hear Then the Parable, p 376). On the other hand, as he acknowledges in the same breath, Luke could have been simply conforming to Roman/urban custom, as he often does (as in Lk 5:19, altered from Mk 2:4). Matthew's "in the field" is clearly his own stereotyped phrase (see Mt 13:36, 13:44, 24:18, 24:40), and Thomas' "tilled soil" is a late idiosyncrasy. William Herzog rightly goes with Mark:
"The seed is sown 'on the land', a reference to the Promised Land... Although this image is preferable to the 'garden' image in Luke, it is possible to read the reference to the garden as an image of the land as a new Eden, in which case the two variants are not so far apart as they seem." (Jesus, Justice, and the Reign of God, p 206)That's a nice way of accommodating Luke "just in case", but it seems safe to view his garden as much a product of evangelical redaction as Matthew's field.(1)
What does the seed grow into?
In Mark's version the mustard seed culminates in "the greatest of shrubs"; in Matthew it grows into "the greatest of shrubs" and then "a tree"; in Luke it grows right into "a tree"; and in Thomas it ends in "a great plant". Matthew and Luke's versions are inappropriate, since a mustard shrub obviously isn't a tree. Mark has it right (Thomas offers a variant), but the question presses: how do we make sense of a shrub that has pretensions to be a tree in two gospels?
The myth originally undermined by Jesus (in Mark) and gradually reclaimed (halfway by Matthew, completely by Luke) is the cedar of Lebanon, an eschatological metaphor for Israel (Ezek 17:22-24, 31:5-6; Dan 4:10-12; Ps 104:10-17) depicting nations humbled in her presence, beasts taking shade under the limbs, birds nesting in the branches. Jesus' mustard shrub is a burlesque, a deliberate mockery of the cedar, though reincarnated into more holiness (the tree) by the time of Matthew and Luke.(2) As Scott explains it, "even though Jesus' parables play against common wisdom, in the end common wisdom frequently wins, removing the parable's fangs" (Hear Then the Parable, p 67).
What's the meaning?
Despite Matthew and Luke's attempts to sanitize, mustard seed is a sacrilegious metaphor for the kingdom, representing uncleanliness and disorder. As Herzog summarizes:
"Once sown, it spreads like a weed, causing havoc on the ordered garden of the land. It also throws purity boundaries into confusion precisely because it spreads indiscriminately, thereby violating the prohibition against planting two kinds of seed in the same field (Lev 19:19; Deut 22:9). The mustard shrub becomes an agent of confusion and source of uncleanliness. The goal of sowing is not to turn it into something it isn't (a tree) but to maximize what it is (a ubiquitous shrub), a force to be reckoned with. Like the land itself, the purpose of the shrub is to provide for others, the birds of the air." (Jesus, Justice, and the Reign of God, p 206)But Herzog marginalizes the future aspect of the kingdom -- and Scott erases it altogether, saying that because "God's mighty works are among the unclean and insignificant" the kingdom "will not meet grandiose expectations" (Hear Then the Parable, p 387). Like most members of the Jesus Seminar, Scott thinks Jesus preached a purely sappiential (here-and-now) kingdom of God. But the mustard shrub points to the apocalypse as much as the cedar of Lebanon. The fact that Jesus' kingdom consists of low-lives doesn't mean it will never meet grandiose expectations, only that it will meet grandiose expectations in surprising ways -- the "reversal of fortunes" manner characteristic of millenial movements.
Like all of Jesus' vulgarities (the Leaven, the Tares), the Mustard Shrub suggests a kingdom of pollution and impurity in which sinners will be vindicated.
1. The Farrer theory makes best sense of the movement assumed here. On Scott's assumption that "garden" is the original, the two-source theory offers the better explanation; but see further.
2. On the two-source theory, we're stuck with "tree" in the earliest source (Luke/Q) instead of the latest. That's what Scott thinks: "The Q tradition clearly saw the reference [to the cedar of Lebanon], and so the shrub became a tree, and Thomas and Mark sense the dilemma and refer to the great and the greatest." (Hear Then the Parable, pp 385-386) Why would the earliest source "clearly see the reference" and sanitize so heavily, but not later sources? Once again, the Farrer theory makes good chronological sense: the movement from "shrub" to "shrub/tree" to "tree" (Mark to Matthew to Luke) shows the Christian movement becoming increasingly clean over time, as all millenial movements do when the apocalypse doesn't come.
Herzog, William: Jesus, Justice, and the Reign of God, Westminster/John Knox, 2000.
Oakman, Douglas: Jesus and the Economic Questions of His Day, Edwin Mellen, 1987.
Scott, Bernard Brandon: Hear Then the Parable, Augsburg Fortress, 1989.
The complete series
The Prodigal Son
The Unmerciful Servant
The Mustard Seed
The Dishonest Steward