[Misericorde]

Judas was one of the 12 apostles. He betrayed Jesus and delivered him to his death sentence basically. Mary Magdelen [the woman who Gaga is portraying/the woman who's side she is telling the story from] was once Jesus' "wife" for all intensive purposes. She ended up betraying Jesus by falling in love with and being with Judas. [This is what the entire song is actually about.]