Not really related to the thread (other than it being loosely related to your post)
I can't say I have ever knowingly listened to Petra, but they are referenced in a very funny song:
The Houseplant Song by Audio Adrenaline
Take two houseplants
And put them to the test
Set them both in front of speakers
And let the music do the rest
The first one you play Mozart
Or something lovely like that
The second one you play that Petra Or that MegaDeth.
Doesn't really matter what kind of rock it is...
He preached that on a Sunday morning 2 days after a bunch of us went to a Mylon Lefevre and Broken Heart concert at our youth pastor's urging but against the head pastor's wishes. :)
Petra isn't the first Christian rock band. Credit should go to either Larry Norman or Mylon Lefevre for creating the first Christian rock album, depending on your opinion of if Norman's album had a Christian enough message to be called Christian. But Petra is the one that bore the heavy criticism from churches and stayed with it long enough to make Christian rock acceptable. In short, they're probably the first Christian rock band that could quit their day jobs.
And if you like good Bible teaching with a classic rock sound (i.e. pre-rhythm guitar like Eagles or Kansas) it's hard to beat early 1980's Petra. I'd be rich if I had a dollar for every time the past few decades I was in a Sunday school class / small group and was able to answer a question about a Bible verse just by remembering a line from one of their songs.
When I'm in the mood for all flavors of rock n roll I can put all of Petra's albums in a playlist and play it by random. Some songs will have a hippie sound from their mid 70's while some songs will have an arena rock sound from late 80's early 90's. Some of their post-retirement recordings have the classic rock sound but with modern recording technology and techniques. It's really good stuff and always encouraging you to stick to Jesus like glue with a no-matter-what, no-matter-who kind of attitude.