Genesis 4:8 Now Cain talked with Abel his brother; and it came to pass, when they were in the field, that Cain rose up against Abel his brother and killed him.
Cain wasnt just chatting with Abel. His jealousy of Abel's sacrifice being excepted by God and his not caused angry words between them. cain, ambushed his brother. Cain commits the 1st homicide. Abel did nothing to cain. Anger left unchecked is a driving force for murder. Jesus ups the standard by saying, if you have anger & hatred in your heart, you murder. I think we are all convicted of that. Yet His forgiveness is gigantic.