Question: “What is the best scripture to give my cousin when she says the devil believes and trembles? She listens to you a lot but always brings this up to me I have tried to answer her the best I can, but she just keeps saying but the devil also believed.”
Answer: It’s difficult to know exactly how your cousin is using James 2:19. In proper context, James is continuing a discussion that faith without works is dead. I recorded an episode on James chapter 2 within its proper context and think that would be helpful here. The chapter is discussing how a believer’s faith is useless to the world if it is not demonstrated by works. The point of the demons believing in God is to say that belief in the existence of God is not what saves a person. That belief must be specifically on the One Who God sent, Jesus. Even more specifically, a person must place their faith in His death, burial, and resurrection for the full payment of their sins to be eternally saved and given the gift of everlasting life.
Demons have not been offered salvation. James 2:19 is not saying that they have believed on Jesus as Christians have believed on Jesus. It is to say that the demons have believed God and they tremble in their knowledge. Works are an extension of a disciplined believer not the proof of a saved person. Many people are saved but do not show their faith by works, thereby rendering their faith dead to the world.
To say that James 2:19 is a proof that believing is not enough is to error from the context. It seems like your cousin is trying to say that works are a proof of a person being saved. I would implore using verses like Romans 11:6 which state that grace and works cannot both be true for the salvation of a soul. I would also suggest asking your cousin to clarify what she means when she uses James 2:19. I would further ask her to describe what she believes a person must do to go to Heaven upon their death. This will give a better idea of what she is trusting in to get to Heaven.