Since he does not seem very religious, and more “spiritual”, I don’t think Bible verses would help, since the Bible is only valuable to one who finds value in it (ie. believes in what it teaches). This is why slinging Bible verses at atheists doesn’t do anything to help your cause, unless they are explicitly trying to point out an apparent “contradiction”.
Instead, you need to come at him with reason.
He says he has his ideas about God, who he is, what he wants, and how he saves. My first question to him would be “What basis do you have for your beliefs?”. This is because even believe needs reason. Any belief isn’t “out of thin air”, it has a reason. And do not accept the answer “It’s just what I believe”, because that just implies that there is no basis or evidence for believing what he believes other than personal laziness. If you are to believe something, there is always a reason why you believe it, such as trusting the word of someone else, or experiential evidence. So, I would try to get him to point out the reasons for his beliefs and show that belief based on emotions or personal “feelings” does not equate to truth, because sometimes personal feelings can cloud the truth, such as a parent that doesn’t/won’t want to accept that his/her son had murdered someone. That would be my step one.
Step two would be to, by reason, work through God’s attributes and why they must be so. You may take aid from C.S. Lewis’s Mere Christianity if you like. This is all to allow him to better understand who God is.
My step three would be to show how God personally interacts with the world and his creation.
Step four, show how God would have interacted with the first humans and how they fell from grace. This is where you may be able to start to use the Bible as a bit of history, even if you do not use it as strict history.
Step five, is to use the Bible to show God’s interaction with the Jews in the OT.
Step six, introduce the NT with Jesus and how his role is necessary and makes sense theologically/philosophically.
Then keep working your way closer to the Truth.
This is, of course, only going to work if he listens to you, or wants to listen (ie. he is curious to learn). You want to do this in charity and patience. Take your time. Don’t necessarily confront him about it, but work it into normal conversations to where he is likely to be more relaxed. If the conversation starts getting heated, stop for a while.
That’s my 2 cents.
