Holy Writ vs sacred writing

Holy Writ and sacred writing both are nouns.

Word	Noun	Adjective	Verb	Adverb
Holy Writ	Yes	No	No	No
sacred writing	Yes	No	No	No

As nouns, sacred writing is a hypernym of Holy Writ; that is, sacred writing is a word with a broader meaning than Holy Writ:

Other hypernyms of Holy Writ include religious text, religious writing, sacred text.

Holy Writ (noun)	sacred writing (noun)
the sacred writings of the Christian religions	writing that is venerated for the worship of a deity