God has set up a system to call, convert, and educate a people for Himself. They are a minority, very few in number. They are not mighty, noble, and learned, but the weak of the world. God calls them and gives them His Spirit and teachers to help them understand. Of all people on earth, only they have a chance to understand the Bible.
The seed represents God's Word communicated in various ways: in preaching, writing, and acts of divine intervention. Those God chooses understand the gospel because it comes only by the power of His Spirit. Without this spiritual power, the hearer is susceptible to having God's knowledge stolen by Satan, the accuser and tempter.
God's Word sometimes falls on the ears of people whose hearts are calloused by sin, on whom it makes no real impression. Like seed on a hard-packed road, it is consumed before it ever has a chance to develop. Such hardened people soon lose interest in Christ's good news and continue in the ways of the world.
Martin G. Collins
Parables of Matthew 13 (Part Two): The Parable of the Sower