Jeffrey Spender is the son of CSM. The son is not impressed with his father's life and is disgusted by the road the father has taken to get to this point. CSM tries to temp Jeffery to come over to the dark side with the power he would have and the knowledge he would possess. CSM wants a heir to his work and since Mulder is not working out the way he hoped he would have to settle for his son. Jeffery rejects his father's offer in the strongest way possible. He shoots him. I would say that is an answer.