In the parable of the sower, what exegetical reasons are there to interpret the third type of soil to be genuine Christians? In the parable of the sower, four types of soil are mentioned.  It seems to be pretty commonly accepted that the first two types of soils represent unbelievers or "make believers".  The fourth type of soil is held to be true believers that are living fruitful lives.  

The debate appears to come in when considering what the third type of soil is--the seed that fell among the thorns.  What exegetical reasons are there to accept that this type of soil does refer to genuine believers who are living apart from the abiding life to which we are called rather than a third type of unbeliever?


  Mark 4: 1-8 ESV
  
  1 Again he began to teach beside the sea. And a very large crowd gathered about him, so that he got into a boat and sat in it on the sea, and the whole crowd was beside the sea on the land.
  
  2 And he was teaching them many things in parables, and in his teaching he said to them: 
  
  3 "Listen! A sower went out to sow.
  
  4 And as he sowed, some seed fell along the path, and the birds came and devoured it. 
  
  5 Other seed fell on rocky ground, where it did not have much soil, and immediately it sprang up, since it had no depth of soil.
  
  6 And when the sun rose, it was scorched, and since it had no root, it withered away. **
  
  7 Other seed fell among thorns, and the thorns grew up and choked it, and it yielded no grain**.
  
  8 And other seeds fell into good soil and produced grain, growing up and increasing and yielding thirtyfold and sixtyfold and a hundredfold."
Mark 4:10-20 explains in a little more detail what 4:1-8 recorded. Jesus is explaining to the disciples the purpose of parables as a whole, and we see that he uses the Parable of the Sower again to describe the people that the disciples will encounter.


  18And others are the ones sown among thorns. They are those who hear the word, 19but the cares of the world and the deceitfulness of riches and the desires for other things enter in and choke the word, and it proves unfruitful.


Initially, the person is hearing the Word (v 18), but desires of the flesh and worldly things make their way in, causing that person to not produce fruit (v 19).