See the notes at Matthew 13:18-23.

The sower soweth the word. Though our Lord thought fit to give the above gentle rebuke to his disciples for their dulness; yet he condescends to favour them with an interpretation of the above parable, which here begins: by this it appears, that the seed in the parable, before delivered, and which fell on different sorts of ground, is the word of God, which was preached to hearers of different dispositions: the word is the word of life and truth; the word of peace and reconciliation; the word of faith and righteousness; the word of salvation; the word which publishes and declares all these to be in and by Jesus Christ.

The sower soweth the word--or, as in Luke (Luke 8:11), "Now the parable is this: The seed is the word of God." But who is "the sower?" This is not expressed here because if "the word of God" be the seed, every scatterer of that precious seed must be regarded as a sower. It is true that in the parable of the tares it is said, "He that soweth the good seed is the Son of man," as "He that soweth the tares is the devil" (Matthew 13:37-38). But these are only the great unseen parties, struggling in this world for the possession of man. Each of these has his agents among men themselves; and Christ's agents in the sowing of the good seed are the preachers of the word. Thus, as in all the cases about to be described, the sower is the same, and the seed is the same; while the result is entirely different, the whole difference must lie in the soils, which mean the different states of the human heart. And so, the great general lesson held forth in this parable of the sower is, that however faithful the preacher, and how pure soever his message, the effect of the preaching of the word depends upon the state of the hearer's heart. Now follow the cases. See on Mark 4:4.