Music is a higher language than religion, so I don't think it really matters what its about as long as it has good riffs. That said... I'm no Screwdriver fan
If the feeling is genuinely sincere in the music, you shouldn't need preachy lyrics to make the point, the music should just make it.
As Drew put it "music is a higher language than religion" but I'd like to add that it's a higher language than pretty much anything else in existence.