This answer is just a brief attempt at the leading question, "What is the meaning of this parable?"
Interest is expressed in Matthew's version of the parable in particular. The "sower and seed" parable appears in each of the three Synoptic Gospels, Matt 13:3-25 // Mk 4:3-20 // Luke 8:5-15, with some variations in the parable and its explanation. This is more a "global" comment, and others may well come in with a different perspective, and some Matthean particulars.
What is a parable? A parable is a story designed to elicit a judgment from the listener -- and that judgment implicates the listener in some action or response.
A powerful example of this is Nathan's story to King David about the poor man and his lamb, which was seized and sizzled by the rich man (2 Samuel 12:1-7). The story provokes an outraged response from David, to which Nathan replies, "You are the man!"
As the Nathan/David illustration already suggests, "parables" have been around for a long time. Although Jesus' teaching is especially associated with parables, he didn't invent them, and others through the centuries have used them.
Jesus and parables. There are probably three main "styles" of parables that the gospels show Jesus as using:
- brief, pithy statements ("The kingdom of heaven is like yeast that a woman took and mixed with three measures of flour until all the dough had risen." Matt 13:33)
- short stories involving several characters and a "plot" (e.g., the "Good Samaritan", in Luke 10:25-37)
- more elaborate "symbolic" stories, accompanied by a "key" (e.g., the parable of the sower, under discussion here).
Clearly, the "definition" of a parable given above has its closest fit with the middle, "short story" parable type. Whether the first and third also are intended to provoke "self-implicating" reaction is open to question, although my own sense is that this approach works well.
The Parable of the Sower
One answer, then, to "what is the meaning of the parable of the sower?", is to enquire further about what kind of judgment it provokes in its hearer(s) - or might provoke!1
The effect of this parable is not so direct as Nathan's story of the poor man's lamb told to King David. One common (?) interpretation can be safely ruled out. It is sometimes said that the message of the parable is that "the word does the work". Now, it may be that this is true (and other parables would make this point more clearly), but it seems unlikely here. At least, if it's the case that "the word does the work", this parable suggests that in the majority (three out of four that Jesus describes) of cases ... it doesn't work! ("He who has ears -- let him hear!" Matt 13:9)
Given the larger setting in all three of the accounts in which it appears, the parable is told to those anxious (?) about their own ability to understand, to be perceptive listeners. Much as King David offered a judgment on the "rich man" that implicated himself, so too Jesus' listeners could not help but align themselves with the "good soil" (case #4) which produced a harvest.
By implication then, the hearer thus aligned with the "good soil" will guard against the other three scenarios: vulnerability to malign spiritual influence, lack of perseverance, and the lure of riches. Or, in a more familiar order and wording: the world, the flesh, and the devil.
The meaning of the parable, then is as much an "action" as a "proposition": it is to provoke the inclination of the hearer towards productive Kingdom living.2
On this reckoning, trying to work out more precise theological questions about "assurance of salvation" or the like is, ironically perhaps, to miss Jesus' main point. His listeners did not walk away pondering this question, but rather whether their understanding of Jesus' message led to a "fruitful life" (Matt 13:23 // Mark 4:20 // Luke 8:15).
Without any doubt, the most significant academic contribution to the study of Jesus' parables in the 20th C came from Joachim Jeremias. His major study The Parables of Jesus came out in English in 1966, and a revised edition in 1972 (this is the one that is still available). He also prepared a "simplified" version, Rediscovering the Parables. There is, of course, a huge literature on the parables, but Jeremias's contribution is pivotal.
- It is significant, of course that the parable of the sower in particular is the context for Jesus' own teaching about the effect of parables: that they can conceal truth from those unwilling to listen, as well as disclose truth to those inclined to hear (Matt 13:10-17 // Mark 4:10-12 // Luke 8:9-10).
- This is, perhaps, a "distinctive" of Matthew's version, as the parable of the sower serves as an introduction to a collection of "kingdom parables" in the rest of Matthew 13.