My Grandpa and his beliefs

My grandpa has this thing where he sings and read about someone named Yhwh and says that anyone that doesn’t believe in that name will be in his quotes “slammed into the pit of fire”. And i just don’t get it he’s always talking about it and saying that jesus is a false name and saying that we are dumb for saying that name. I asked my grandma what he was; baptist or one of the things but she says he’s mostly baptist. I’m very confused on the whole thing and would love some help.