A popular concert song of theirs was not allowed on their first album because of the "controversial" title and lyric: "Killing my old man; you may not understand, he's a terrible man."
Petra wasn't recommending patricide, of course. They were putting to music a thought expressed by the apostle Paul in Romans 6:6..."For we know that our old self was crucified with [Christ] so that the body of sin might be done away with, that we should no longer be slaves to sin." (NIV)
The idea is, if I'm going to be a Jesus kind of person, I need to stop being a devilish kind of person, full of pride and Doing Things My Own Way. In the Aramaic Bible in Plain English's translation of Ephesians 4:22, Paul restates it like this: "You should put aside from you your first way of life, that old man, which is corrupted by deceitful desires."
Paul puts it even more plainly in Galatians 2:20: "I have been crucified with Christ." And that is exactly what Jesus meant when he said, "If anyone would come after me, he must deny himself and take up his cross and follow me." (Matthew 16:24, NIV)
Truth is...Tim Rice and Andrew Lloyd Webber had it right in Jesus Christ Superstar when they had Jesus singing, "To conquer death, you only have to die."
P.S.: "Killing My Old Man" made it onto a subsequent album ("Never Say Die"). Thanks to YouTube, here it is: