Maybe the 'correct' angle isn't in the 'front door' so to speak. That is to say, since your friend is christian, maybe the move isn't to run up in the core of his belief system. It's like trying to knock down a mountain with a toothpick. Instead, maybe focus on either the things you have in common, or the things that he might enjoy learning about.
These things, despite how not connected they may seem, I'm sure people on here can show you the connection back to the church....
If you are certain of your friendship with him and he is open minded enough, and this is the only way you can conceive of talking with him, you may start with showing him our English(angle ish) language(lung gauge) and how each letter is in fact a hieroglyph of sorts. The Esoteric Alphabet is a nice place to start. Then again, if you aren't familiar with it entirely, maybe you should 'know' first before you explain.
There are a ton of variables, but if you want some suggestions feel free to message me. Also, maybe just get him on the site, let him dig around and tell him to feel free to get on the chat and ask some questions.
I recommend you read up on the Dogons, they are a fascinating tribe in Africa that have remained largely unpolluted by outside change, they have practices and knowledge that goes back thousands of years. The Dogon use hieroglyphs that are similar2 those found on the monuments of Kemet (Egypt) and can be cross referenced that way. A gentleman by the name of Laird Scranton can help navigate if you youtube his name.
There is no way2 know for certain if any of that is decoded correctly, use your intuition and thorough study.