Q. You say in your comments about the Parable of the Sower that people with the heart for Jesus will hear the parable and understand. The disciples, I would think, had a heart for Jesus, yet they asked Jesus to explain the parables. So why were their ears not open to understanding the meaning of the parables?
The disciples needed to get a start somewhere. They needed to know that the stories Jesus was telling in his teaching had a meaning deeper than the surface-level meaning. The point of the Parable of the Sower wasn’t just that farmers should be careful where they sowed their seed, because it wouldn’t grow well in some places. Jesus was really talking about his own message and how people would respond differently to it based on the state of their hearts.
Significantly, when the disciples ask Jesus to explain this parable, he responds, “Don’t you understand this parable? How then will you understand any parable?” In other words, this parable is a key to all the other ones. It is a parable about parables. It has been called a “meta-parable.” Once Jesus explained its meaning to the disciples, then they realized that they would need to try to understand the deeper meaning of such stories.
This took time. The disciples needed to learn how to recognize these meanings. And Jesus took the time to teach them. Mark says at the end of the section in which he relates the Parable of the Sower and other parables, “[Jesus] did not say anything to [the crowds] without using a parable. But when he was alone with his own disciples, he explained everything.”
It was precisely because the disciples’ hearts were open to Jesus that they were able to benefit from this instruction. If their hearts had been hard, the stories would have remained just stories to them, with no meaning deeper than what was on the surface.
For his part, Matthew records in his gospel this interesting exchange between Jesus and his disciples, similarly at the end of a section in which he relates Jesus telling many parables:
“Have you understood all these things?” Jesus asked.
“Yes,” they replied.
He said to them, “Therefore every teacher of the law who has become a disciple in the kingdom of heaven is like the owner of a house who brings out of his storeroom new treasures as well as old.”
This shows that the disciples were catching on to the meaning of the parables, and, as Jesus notes, as a result, they were understanding how the new things that he was bringing fit in with what God had been doing all along.
This would not have been possible if their hearts had not been open to Jesus. That was a necessary condition, but we see that it was not a sufficient one. Jesus also had to get them started on how to understand the parables using their open hearts. We can be grateful that the gospels record Jesus’ explanations of several of his parables so that we can have the same benefit ourselves. We just need to make sure that our hearts are open, too.
Good Question 
What questions do you think the disciples wanted to ask Jesus about the parable of the sower?
Something like, “What does it all mean? Why do you tell stories like that?”