What is Christian

I had an interesting conversation with a friend this morning.  He is a very good man, I respect him very much but sometimes I'm not sure I agree with him.  Today we were talking about a concert series he went to and took some kids to see.  It was a Christian concert series but one of the bands was a metal band.  They had very dark props and portrayals that bothered him and the music was dark but not anti-God.  He made the statement to me "That was not Christian".  To which I had to ask "Why not? What makes it Christian or not Christian and who are we to judge?"  As we learn from the Bible there is a sense of relativity to alot of things.  To the Jews it was wrong to eat certain meats but the Gentiles didn't see any issue with that so they could eat the meat.  Other times in the Bible the sentiment is upheld that if it is sin in your heart, it is sin for you, even if it's not necessarily wrong.  To my friend, it was wrong, that music was not good.  To others, coming from a more mainstream or secular music, this may have been a step towards the light for them and this may have in fact been a good Christian experience. So before we judge things I think it's important to remember our experiences and perspectives may not be the same as another persons.