"'Still others, like seed sown among thorns, hear the word; but the worries of this life, the deceitfulness of wealth and the desires for other things come in and choke the word, making it unfruitful.'" NIV translation
The seed that is sown among thorns lives and produces a plant but the plant does not get enough sun or water and nutrients to mature and produce fruit. This speaks of the person that is saved but does not put their faith into action and serve. They go through life without telling anyone else about Jesus.
"'Others, like seed sown on good soil, hear the word, accept it, and produce a crop - thirty, sixty or even a hundred times what was sown.'" NIV translation
The final seed not only sprouts and becomes a growing plant but, in its life, it produces fruit. A seed that does not produce fruit really has no purpose as, when the plant dies, there will be nothing left to show that it even existed on the earth. We see, here, two groups of three and are reminded that the number three is associated with the earthly display of God's will. The first group of three speaks of the life of a Christian while the second group speaks of the judgment of the seed. Any farmer will tell you that they judge the quality of a seed by how much fruit (grain) they harvest in the season. This speaks of the judgment of believers where our work on the earth is judged and our rewards are given.
"He said to them, 'Do you bring in a lamp to put it under a bowl or a bed? Instead, don't you put it on its stand? For whatever is hidden is meant to be disclosed, and whatever is concealed is meant to be brought out into the open. If anyone has ears to hear, let him hear.'" NIV translation
Now, Jesus uses a question and answer to further explain the message of the sower. We see that a lamp that does not share its light has no value just as the seed that does not produce any fruit. Putting the lamp under a bowl is a conscious decision to remain in the dark (ignorant). We see that God does not want us to be ignorant as Jesus tells us that the things that were hidden before are revealed through Him. He also gives them a danger sign as He speaks of "ears to hear". We must understand that Jesus was a Jew speaking to Jews and, when the word "hear" is used, it means putting into action what they have heard with their ears and mind. We are reminded that, when we have the light of Christ within us, we have a responsibility to let that light flow out of us and not willfully hide it under the bowl.