The "someone at the door" is responsibility. It could be his own personal health, mental state, spiritual development, outside obligations, or really anything. Whatever is at the door is in need of attention, but he is too engrossed in his own thoughts and torments. He likes to entertain them, either in just a figure of speech sort of way (entertain a thought) or possibly through the songs that he sings.
Basically the metaphor is that he locks himself up in a house of negative thoughts and shuts out the world.
The "someone at the door" is responsibility. It could be his own personal health, mental state, spiritual development, outside obligations, or really anything. Whatever is at the door is in need of attention, but he is too engrossed in his own thoughts and torments. He likes to entertain them, either in just a figure of speech sort of way (entertain a thought) or possibly through the songs that he sings.
Basically the metaphor is that he locks himself up in a house of negative thoughts and shuts out the world.