IJesus Christ, the Only Begotten Son of God, Who was born of the Father before all ages; God from God, Light from Light; true God from true God, begotten, not made and is consubstantial with the Father would not write a book. He didn't then and He wouldn't now.
You see, Christianity is a not a religion of the Book. It is a religion of the Word and that Word is Jesus Christ. And Jesus “Lord and God” as Timothy said in John 20:28.