But really, I don't claim to be speaking for God in that way. God spoke for Himself and the people He spoke to were inspired to record it. It is not secret knowledge, it is right there for anyone who cares enough to pursue it.
Some common tests used to determine if the person behind the book was really inspired by God are 1) Ability to do miracles authenticates their message 2) They give prophecy that is later fulfilled or 3) Prophecy by someone who met #2 was givne and they fufilled it.
Take care.