Cain remains the dominant man. Abel comes along. Although the author of this chapter is brief in his description, it is clear that Cain is up to something. They go to the field, a place where they are all alone. No one can stop Cain if he carries out his plan there. Animals kill instinctively (out of fear, for example) or to satisfy hunger. Man is a rational being. He also uses his mind for evil. Man's strong points take him deeper into evil, if he gives in to it.
8 Cain spoke to Abel his brother. And when they were in the field, Cain rose up against his brother Abel and killed him.