morality is subjective and people don't have free will

[Angrboda]

Why can't it come from both?

We clearly have a built in moral compass--which the Bible also recognizes: 

Romans 2:12 For all who have sinned without the Law will also perish without the Law, and all who have sinned under the Law will be judged by the Law; 13for it is not the hearers of the Law who are just before God, but the doers of the Law will be justified. 14For when Gentiles who do not have the Law do instinctively the things of the Law, these, not having the Law, are a law to themselves, 15in that they show the work of the Law written in their hearts, their conscience bearing witness and their thoughts alternately accusing or else defending them, 16on the day when, according to my gospel, God will judge the secrets of men through Christ Jesus.

In addition to the moral laws/instruction laid out in Exodus/Leviticus and in the NT, there are also other doctrines that lead to conclusions about human value, responsibility, and relation to the natural world.

Would you follow a moral from the book if it didn't agree with your gut?