The following is taken from a book entitled For the Love of God by D.A. Carson.
The so-called parable of the sower (Mark 4:1-20) might better be called the parable of the soils, for the variable that gives the parable life and depth is the variation in the land onto which the seed is thrown.
Because Jesus provides the interpretation of His own story, its primary emphases should not be in doubt. The seed is the “word,” i.e., the word of God, which here is equivalent to the Gospel, the good news of the kingdom. Like a farmer scattering seed by hand in the ancient world, this word is scattered widely. Inevitably, some of the seed falls on ground that for one reason or another is inhospitable: perhaps it is the hard-packed dirt of the path, or perhaps birds come and eat the seed before it settles into the plowed ground and germinates, or perhaps it grows in the shadow of thornbushes that squeeze the life out of it, or perhaps it germinates in shallow soil with limestone bedrock just beneath the surface, such that the roots cannot go down very far to absorb the necessary moisture. The parallels with the way people hear the word are obvious. Some are hard and repel any entry of the word; others are soon distracted by the playthings Satan quickly casts up; others find that worries and wealth–the terrible Ws–squeeze out all concern for spiritual matters; still others hear the word with joy and seem to be the most promising of the crop, but never sink the deep roots necessary to sustain life. But thank God for the soil that produces fruit, sometimes even abundant fruit.
So much is clear enough. But two other features of this parable deserve reflection.
The first is that this parable, like many others, adjusts the commonly held perspective that when the Messiah came there would be a climactic and decisive break: the guilty and the dirty would all be condemned, and the righteous and the clean would enjoy a transforming rule. That is what the final kingdom would be like. But Jesus pictures the dawning of the kingdom a little differently. In the parable of the mustard seed (Mark 4:30-32), for example, the kingdom is like a tree that starts from small beginnings and grows into something substantial; here is growth, not apocalyptic climax. So also the parable of the sower: for the time being, the word is going to be scattered widely, and people will respond to it in different ways, with widely divergent yields.
The second is that not all of those who show initial signs of kingdom life actually take root and bear fruit. That truth deserves meditation and calls for self-examination.