They sing about the kind of people that they think should be admired. They will even sing the praises of ruthless ambition and flagrant immorality, in order to glorify and dignify their own sins. The purpose of all music is to praise, honor, or dignify whatever the music is about. Poetry is the same. A song or a poem about suffering or sorrow gives the moans and cries of humanity more significance than the squealings of a wounded beast.
Religious music is a form of worship.
Every religion also has it's own poetry, and catch phrases, which are meant to identify and honor the god of that religion. Christians often do this same thing to each other. It is like unto children sitting in the markets, and calling unto their fellows, 17. Just because someone uses familiar religious phrases doesn't mean that we truly have the same religion. If you don't want to embrace or shake hands, they accuse you of lack of love, or pride, or schism.