religious writing vs sacred writing

religious writing and sacred writing both are nouns.

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

As nouns, religious writing and sacred writing are synonyms defined as:

religious writing and sacred writing: writing that is venerated for the worship of a deity

Other synonyms of religious writing include religious text, sacred text.

religious writing (noun)	sacred writing (noun)
writing that is venerated for the worship of a deity	writing that is venerated for the worship of a deity