Good Book vs Holy Writ

Good Book and Holy Writ both are nouns.

Word	Noun	Adjective	Verb	Adverb
Good Book	Yes	No	No	No
Holy Writ	Yes	No	No	No

As nouns, Good Book and Holy Writ are synonyms defined as:

Other synonyms of Good Book include Bible, Book, Christian Bible, Holy Scripture, Scripture, Word, Word of God.

Good Book (noun)	Holy Writ (noun)
the sacred writings of the Christian religions	the sacred writings of the Christian religions