Word of God vs Book

Word of God and Book both are nouns.

Word	Noun	Adjective	Verb	Adverb
Word of God	Yes	No	No	No
Book	Yes	No	No	No

As nouns, Word of God and Book are synonyms defined as:

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

Word of God (noun)	Book (noun)
the sacred writings of the Christian religions	the sacred writings of the Christian religions
the message of the Gospel of Christ	the sacred writings of Islam revealed by God to the prophet Muhammad during his life at Mecca and Medina
a manifestation of the mind and will of God