The Gospel is the Only Word of God in the Entire Christian Bible

When do we say a statement-written or oral-is 'Word of God'?
Any statement spoken by God is Word of God. For instance, being Son of God, anything Jesus says is Word of God.
On the other hand, any statement spoken by man is word of man.
The book will explain and prove 'Why is the Gospel the only Word of God in the entire Christian bible.'
Happy reading!