sacred writing vs religious writing

sacred writing and religious writing both are nouns.

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

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

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

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

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