I've thought about it a lot and I've realised why Christian Music is generally musically so bad, despite the fact that there have seen songs with Christian themes(Bob Dylan comes to mind, as do the musical project Enigma) that have not been half bad.
One of the big reasons why Christian music isn't great is obviously because it's written only for Christians; who may be common, but Christians who want to listen to Christian Music are not. This cuts your market down immensly more than any other genre.
Another thing is that songs are written about something - but also take other things into account. Christianity is very unified in it's theme, so all Christian songs are not only going to be about the same thing, but each song is gooing to be narrow in their scope. Writing a song "about something" usually leaves it kind of drab and unoriginal. You need to draw other aspects into it.
Then you get bands like Inkubbus Succubus. However, non-pagan fans enjoy them. Why? Because Pagan based music usually can be appreciated for it's mythological, adventerous or generally spiritual aspect, and the writers keep that in mind. There is no such equivillent in Christian music.
A very important point about why Christian music is kinda rubbishy is this - you can't sing about a cup of Coffee, it must be JESUS'S cup of coffee. The unified nature of Christianity may make for a good belief system for some people, but it does not lend itself to inspired lyrics.
What if someone wrote an entire album about apples, because they like apples? It may turn out good, but likelyhood is it will be a novelty and nothing more.
Christian music reeks too much of the "Us Too!" Christian attitude, where many Christians feel the need to "catch up" with the modern world by "joining in" with things(I think Creationism was borne out of this attitude) as they don't want to feel left out. However they fail to realise they're not being left out. Christians can listen to rock music and metal music if they want, some of it may even have slightly religious instead of anti-religious themes if they look hard enough. I think this is a problem with Christian mentality, this doesn't mean that Christians are BAD as someone is going to quote me on it, just that a lot of people that follow the religion may have this emntality. They don't realise that they're still a majority and not being left out of anything at all - places have just often become places where religion shouldn't apply because it leaves
other people out. There isn't really a huge need for "Christian Death Metal" for this reason.
Why not just be Christians who make Death Metal?
Now, going on to why Christian themed music as opposed to Christian music can be okay, first of all it's because it's not as blatant. This is also why pop music sucks. The whole point of good songwriting is that you're meant to be a word smith, and find new ways of saying things. Both Christian music and Pop music don't bother with this - they just say what they think fits the theme of the song, as long as it rhymes once in a while it's good. Poetry will never consist of "Hey, did you see that guy today? Yeah him. He was really cool wasn't he because he did that thing with the torch-eating? Pretty cool guy, if you ask me", but that's the exact reflection of the methods used in "Pop" music as well as much "Chrisian" music.
This also leands to Christian music being very poppy - never a good thing.
You can't really find your own interpretation in Christian music. It is what it is. There are no subconcious idioms weaving their way into the song structure. Like muchpop music, it is what it is. Because this, you cannot "find yourself" in Christian music like you can other music. If you're a Christian - you'll find that, but nothing more about yourself.
Third is the atmosphere of the music - which has aspects of information. Bob Dylan wrote some very christian songs but he didn't sing them in a "Jesus, Jesus!" atmosphere.
Music is meant to be "spiritual" - but it's not very spiritual. Listen to Enigma(which has some Christian themes in it, interestingly, yet they're still one of my most listened to "Bands" lately, if you check
http://www.last.fm/user/drael), that's "spiritual". If it's something to do with the Soul, it should have a spine chilling, absorbing, magical atmosphere; New Age music often is this.
Enigma is spiritual sounding, Faith and the Muse are spiritual sounding, Rhea's Obsession are spiritual, Dead can Dance are spiritual; Joey John McJesuslover is not spiritual. I doubt there's much New Age Exclusively Christian music out there.
Christian music is often more dogmatic than it should be, singing about some specifics of religion, whereas "spiritual" music is just the idea of the depth of the human soul in general. Christian music doesn't seem to have that element, missing the point. You don't sing about your soul. You make music about your soul.
"Soul" Music by this extension is one of the worst named musical genres in history. It is not "Soul" music, it's cheery shouting out clap along stuff. That's not what "Soul" is made of.
A more realistic or absorbing atmoshphere is something Christian music is lacking; which brings me to ;
emotion. PErhaps the most important one of all. Christian music is just sickeningly happy. It doesn't talk about the struggles of life and love and hoping jesus will answer your prayers but admitting how bleak the world is very often. Sad music is usually better than happy music because we all like sympathy for our problems in some form or another.
So, don't be afraid to think that Christian music sucks, even if you're a Christian. There are real musical reasons why it usually isn't very good, but technically speaking, could be if they tried.