Gospel vs Word of God

Gospel and Word of God both are nouns.

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

As nouns, Word of God is a hyponym of Gospel; that is, Word of God is a word with a more specific, narrower meaning than Gospel:

Gospel: the four books in the New Testament (Matthew, Mark, Luke, and John) that tell the story of Christ's life and teachings
Word of God: the message of the Gospel of Christ

Gospel (noun)	Word of God (noun)
the four books in the New Testament (Matthew, Mark, Luke, and John) that tell the story of Christ's life and teachings	the sacred writings of the Christian religions
	the message of the Gospel of Christ
	a manifestation of the mind and will of God