Do not get gentle into the night

The story by Dylan Thomas Do not go gentle into the night was an interesting story. It was about a son who wished his father would keep on living and not die. The story was really sad just painted a picture in my head of what the main character was going through with his father. In one of the lines in the story it says " Rage,rage against the dying of the light". I believe the narrator is trying to explain that the light is bad and to fight against it. I think it is a important line because it is repeated through out the story. Another line that is repeated throughout the story is "Do not go gentle in to that good night". I thought about what exactly is the narrator trying to say in this line. Why is the good night reffered to as being bad in this line? It seems to me that he is trying to say that he does not want his father to go to internal sleep which is death.