If one injures another person receives a monetary punishment. One who strikes his father or mother deserves the death penalty. Only then does the Torah return to the story of the Blasphemer and relate that the people actually put the Blasphemer to death. This does not seem to be a smooth flow of narration. The Sefer Darchei Mussar suggests that this sequence of the pasukim contains a tremendous lesson.
Some people feel that a dichotomy exists among Jewish laws.
There are laws that relate to the relationship between man and G-d, and there are laws that relate to the relationship between man and his fellow man. And never the twain need meet. I can be the perfect gentlemen and citizen, and yet deny the existence of HaShem. I can be the most ethical and upright of individuals without a G-d. The Torah is telling us that this is not true.