The main point of Matthew's version of the parable of the sower is to offer an explanation. In order to see this, one needs to review the narrative logic of the entire Gospel to this point.
The first four chapters of Matthew introduce us to the main character, Jesus. They tell us who he is--Son of David, Son of God, Messiah--and how he came into the world, how his ministry got started, etc.
Next we have chapters 5-7, the sermon on the mount. Here are collected Jesus' ethical teachings, the demands he made of both the disciples and Israel--do away with anger, forsake oaths, turn the other cheek, love enemies, and so on. Next come chapters 8-9. Here the focus shifts from word to deed, and we see Jesus' compassionate healing work in Israel. In other words, if chapters 5-7 recount the sorts of things that Jesus said, chapters 8-9 tell us primarily the sorts of things that he did.
Following this is chapter 10, the missionary discourse, where Jesus commissions his disciples and instructs them to say what he has said and to do what he has done: "As you go, proclaim the good news, 'The kingdom of heaven has come near.' Cure the sick, raise the dead, cleanse the lepers, cast out demons" (10:7-8). In short, the disciples are to say and to do what Jesus has said and done in the previous chapters. As 10:25 has it, "it is enough for the disciple to be like the teacher, and the slave like the master."
The chapters on the words and deeds of Jesus (5-9) and the words and deeds of the disciples (10) lead up to chapters 11-12, which record primarily the response of "this generation" to John the Baptist and Jesus, especially its reaction to "what the Messiah was doing" (11:2). This is what the material on the Baptist (11:2-6, 7-15, 16-19) is all about as well as the woes on Galilee (11:20-24) and the conflict stories in chapter 12 (1-8, 9-14, 22-37, 38-45). Unfortunately, it all adds up to an indictment: many of the people, under the sway of their hard-hearted leaders, have decided not to join Jesus' cause.
Given that the eschatological expectations of Judaism envisage--and indeed are all about--the salvation of God's people, the failure recorded in chapters 11-12 poses the same grave problem as does Romans 9-11: How is it that so many in Israel have rejected the Messiah? How did his own receive him not? Chapter 13, which opens with the parable of the sower, addresses the issue. It supplies a sort of mini theodicy--not a solution to the problem of evil in general but a solution to the rejection of Jesus in particular. The chapter teaches that there can be different responses to one and the same message (13:1-23), that the devil works in human hearts (13:24-30), and that all will be well in the end (13:31-33, 36-43, 47-50). Read in its larger context, the whole chapter grapples with the Messiah's unexpected reception, or rather lack thereof.
Just as alleged solutions to the problem of evil never come close to answering all of our questions, so is it with Matthew 13. We may grant the important point that different people respond to the very same message differently, but then why is the devil successful with one person, unsuccessful with another? What are the root differences between those who sprout up and quickly fade and those who stay the course? Why is it that some are not overcome by worldly cares and others get lost in making money? Human beings are containers of mystery, and Matthew 13 does nothing to undo that.
Although the parable of the sower is first of all a sort of explanation of what happened when Jesus appeared in Israel, it implicitly exhorts believers (who should recognize a bit of themselves in all four seeds) to join the fourth sort of hearer, represented by the good seed. For many of us, this may mean above all heeding v. 22, which speaks of the seed that fell among thorns and how "the cares of the world and the lure of wealth choke the word, and it yields nothing." We are likely to respond that we must, if we are to be responsible, worry about money, because without it we will not have food, drink or clothing, nor will our loved ones. How can we not serve God and mammon (6:24)? How can we not worry about our lives, about what we will eat or drink or what we will wear? Will God really take care of these matters for us (6:25-34)? How can we not worry about tomorrow, or suppose that tomorrow will take care of itself (6:34)?
Perhaps it will help to remember the story of Jesus' burial in 27:57-61, for this labels Joseph of Arimathea as both a rich man and a disciple, as well as 6:2-4, which presumes that Jesus' hearers will have money to give alms. If we are to interpret Matthew by Matthew, it would seem that Jesus calls only some to abandon their livelihood and do away with money altogether.
Yet the lesson for everybody else is still radical: riches are seductive and dangerous and can readily become an obstacle on the way to God. Even when we seek to use wealth for good, we too often end up being its slave rather than its master. We become like the rich man in 19:17-22, who could not follow Jesus because in truth he did not own his possessions: they rather owned him. While our gospel does not demand poverty of all, it does require freedom from whatever hinders obedience. So although we may find, living as we do in a modern capitalistic society, that it is seemingly inevitable to make friends of "dishonest wealth" (Luke 16:9), we must not be seduced into amassing goods because we find security in them. Our security needs to lie elsewhere; and our use of money must be determined by Jesus' demand to love God with all of our hearts, souls, and minds and our neighbours as ourselves.