In the Bhagavad-gita the religious principles are divided into three categories: in the modes of goodness, passion and ignorance. Generally, all so-called principles are in the modes of passion and ignorance. Maybe there are some moral instructions, but moral instructions without God-consciousness is impossible to follow. In another place the gentleman quotes one book written by Prof. Charles Smith. The book’s name is “The Paradox of Jesus in the Gospels”. In this book it is admitted that all the statements in the Bible are not directly spoken by Jesus. Some of them are staged through the mouth of Jesus Christ; and specifically this passage: “I am the way, the Truth and the light. No man comes unto the Father but by me.” This gentleman admits that it is put into the mouth of Jesus because that is the literary convention of the author of the 4th Gospel. Such kinds of observations definitely suggests that there are many passages in the Gospel which are later on set up to be spoken by Lord Jesus Christ, but actually they were manufactured by different devotees. So far as Bhagavad-gita is concerned, we do not find any such thing. Everywhere it is stated sri bhagavan uvāca: the Supreme Personality of Godhead said. And all the acaryas have accepted these words as they are spoken by the Lord. No authorized acharya has ever commented that it was put into the mouth of Krishna by Vyasadeva or Sanjaya or any other person.
Ref >> Srila Prabhupada Vani.