There are many people who enjoy heavy metal music that Christian metal bands produce. There is nothing inherently wrong with any music produced by committed Christians who desire to communicate biblical truth—Christian heavy metal music deals with the dark themes of death, pain, and spiritual warfare from a Christian perspective.
While there are some who feel that the heavy, rhythmic bass, frenetic percussion, and high decibel levels of metal music have a negative effect on a person’s spiritual self, that is a controversial view without evidence. Unless the lyrics celebrate sin, the music itself is not sinful. This applies to Christian heavy metal music as well as to country, jazz, rap, pop, reggae, bluegrass, etc.
The problem with Christian heavy metal music is sometimes one of association. In the hands of the unsaved world, heavy metal almost always embraces death and pain and suicide and drugs and anger (metal is very rarely “happy music”). Believers have to be careful not to get sucked into the culture of nihilism and antisocialism that metal usually promotes. While it is true that pain and death are a part of life, the key to overcoming those things is not anger or suicide or revenge. The answer is the gospel of Jesus Christ (Romans 1:16). There is nothing in the Bible that praises or glorifies death in the least, so neither should our music. Lyrics that violate biblical guidelines or celebrate or exalt sinful conduct are not appropriate for Christians.
With any kind of music, including Christian heavy metal, we must ask, “Is the music glorifying Christ, or does it glorify anger, lust, demonism, or some other sinful thing?” The style of the music is really irrelevant. It’s what the music communicates to our hearts and minds that matters, either through lyrics or even through the notes and instruments themselves. No style of music is actually “wrong”; it’s what the musicians do with the music that makes it either “right” or “wrong.”
Regardless of the genre of music one listens to, the believer is to exalt Christ. Philippians 4:8 gives us the description of what should be on our minds: “Whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable—if anything is excellent or praiseworthy—think about such things.” If heavy metal produced by Christian musicians falls under this description, then whether or not you listen to it is simply a matter of musical taste.