It could be about vampires. There are some stories about vampires living in the catholic church to get easy prey. I think it's a commentary on the the last supper though. Christians drink the 'blood of Christ', hence the 'human wine'. To drink the wine is to be forgiven of sin. It could be a comment on the use of the ritual. It's been used as a ritual to 'just forgive sin' and not to repent. A few hundred years ago, it was necessary to see the ritual being preformed, to be a good christian. So not everyone went to church but just watched. A very explicit song, which could display the need for the ritual people have. But then use it as if they are vampires, just wanting the blood, so they are forgiven and are then satisfied and glad Christ saved them, and just continue on living like dark creatures.