Matthew 13:20-21 (NIV)
20 The one who received the seed that fell on rocky places is the man who hears the word and at once receives it with joy.
21 But since he has no root, he lasts only a short time. When trouble or persecution comes because of the word, he quickly falls away.
What is the matter with this heart? It is rocky. But don't think of it as soil containing a lot of rocks. The idea here is that there are a few inches of earth on top of a broad shelf of bedrock.
The key our Lord gives us here is that "he has no root in himself." This is what we would call a shallow life, one that is flitting from this to that, from one experience to another, never content with anything for very long.
The word Jesus uses to describe this kind of person is, literally, "seasonal." There are many people like that. Let there be a crisis, another 9/11, or some major catastrophe that startles them into reality—they will come running to God. When the season changes they will drop right back. They will not continue; they are seasonal. They live on the surface, they are emotional. There is no depth in their life; nothing goes deep into their heart.
Jesus illustrates the terrible danger of a shallow heart, a heart that does not want to evaluate and go deeper but is always living on the surface, it is always relating to the event of the moment and concerned only with that.
The emotional seasons of life will make it very difficult for him to receive the word of God, which changes his heart.