It would be nice if people developed their personal beliefs from the Bible, and only from the Bible. But that’s just not the world we live in.
The reality is that people have experiences, they make choices, they have behaviours that they like doing. And its these pre-existing behaviours that end up influencing, shaping and even defining what they believe about certain things. The classic example is the adulterer who says something like, “I believe God is all about love. God doesn’t want me to be in a loveless relationship. I believe God’s put this other person in my life to experience the joy he designed me to have”. These people don’t think they are pretending. They honestly believe these things to be true. They will even defend them from the Bible.
You do this. I do this. We all let our cherished behaviours dictate and shape our beliefs about God.
How do you respond to someone who does this? Well, neither their behaviours or their interpretation of the Bible are “moveable”. Maybe the best bet is to help them be open to the idea that they have let their behaviours define their theology. Open them up to the heart of the error, and pray for God to graciously soften hearts.