Something that just came to me- we see that Ren is pulled to the light, so he prays to Vader’s mask to help him stay down the dark path.
Does he know that Vader eventually turned to the light? Maybe if he continues to worship Vader and his mask, he will be pulled to the light?
I was reading a comment about this. Some believe Snoke is tricking Kylo by exploting the story of Vader. Vader never has spoken to Ben via the helmet or any other relics. Instead, Snoke is making it seem as if Vader speaks to Kylo Ren. Manipulating Kylo Ren into thinking Vader was this tragic hero that was under-appreciated or some shit. You could say that Luke probably already told Ben about Vader’s redemption. However, I don’t think Luke would freely boast about Vader to his new and training Jedi, including Ben. It’s a dark and emotional thing for Luke to bring up. This is of course is Luke’s flaw and allows Snoke to feed into Kylo Ren’s mind that Luke is trying to hide the ‘true’ story of Vader.