The first verse of our reading is key, especially when taken in the context of yesterday’s readings. Why didn’t the disciples understand this parable? Because they were not able to understand the things of God unless God Himself (by the power of the Holy Spirit) revealed it to them. In the same way, we are unable to believe or understand God’s Word by our own strength, but by the power of that same Spirit.
Jesus goes on to explain the parable of the sower in answer to the unasked question “why don’t everyone believe?” The answer is simple, satan prevents some from believing, some believe then fall away in difficult times, while others believe but then lose the faith due to the distractions of this world. But notice those that remain in the faith. They are fruitful, doing the will of the Father in their day to day lives.
Who is this Jesus? The object of our faith! The very Word of God that is sown in our hearts.