Gospel vs religious writing

Gospel and religious writing both are nouns.

Word	Noun	Adjective	Verb	Adverb
Gospel	Yes	No	No	No
religious writing	Yes	No	No	No

As nouns, religious writing is a hypernym of Gospel; that is, religious writing is a word with a broader meaning than Gospel:

Gospel: the four books in the New Testament (Matthew, Mark, Luke, and John) that tell the story of Christ's life and teachings
religious writing: writing that is venerated for the worship of a deity

Other hypernyms of Gospel include religious text, sacred text, sacred writing.

Gospel (noun)	religious writing (noun)
the four books in the New Testament (Matthew, Mark, Luke, and John) that tell the story of Christ's life and teachings	writing that is venerated for the worship of a deity