Gospel vs sacred writing

Gospel and sacred writing both are nouns.

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

As nouns, sacred writing is a hypernym of Gospel; that is, sacred 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
sacred writing: writing that is venerated for the worship of a deity

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

Gospel (noun)	sacred 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