Better question.
Why didn't God write a rule book himself?
And if he himself was actually Jesus, like some claim. Then why didn't he write a rule book then?
It seems to me all books of God favor the nationality of its origin.
It also seems odd that they all favor men over women.
The Rule Book is known as The Ten Commandments.
Yeshua stated that the greatest of the commandments was to love God with all your heart and soul and the second greatest was to love your neighbor (fellow man). Thus, by keeping these two commandments you would be able to fulfill (be obedient) to all the laws. For by loving God you would respect His Sovereign rule and guidance in your life and by loving fellow man, you would not murder, hate, covet, steal, cheat, nor commit unlawful acts against one another in any way.
Problem with humanity is that we aren't able to abide by even those Two Commandments. And if you think you have, think about your own mother, father, brothers and sisters. Most people have family quarrels and disagreements within their own immediate family - and we think we can bring peace to this world - without God???
Then one of them, which was a lawyer, asked him a question, tempting him, and saying, Master, which is the great commandment in the law?
Jesus said unto him,
Thou shalt love the Lord thy God with all thy heart, and with all thy soul, and with all thy mind. This is the first and great commandment. And the second is like unto it, Thou shalt love thy neighbour as thyself. On these two commandments hang all the law and the prophets. (Matthew 22:35-40)
God Did For Mankind What Abraham Was Going To Do For God.