What Should I Say to Active Churchgoers Who Reject the Trinity and the Deity of Christ?

Questions about what to say to longtime, active churchgoers who don’t believe in the Trinity or the deity of Christ, and a challenge to the idea that it’s possible for someone to have a relationship with Jesus today.  

• What should I say to family members who have been active churchgoers for 40 years, but who don’t believe in the Trinity or the deity of Christ?
• Do you claim to have a relationship with Jesus—someone you never met—who died 2,000 years ago and hasn’t been seen since? That seems like the definition of a delusion, an imaginary friend in the sky.