A short one tonight, and one that will be no new great idea for you, but I was thinking about this whilst mowing the lawn and listening to some early Reasonable Doubts podcasts.
Essentially, there is little moral clarity in the Bible, and even when it gives seemingly clear instructions, like in the 10 commandments, these need contextualising and interpreting. For example, theologians accept “thou shalt not kill” but still arrive at just war theory.
When the reader is commanded not to eat shellfish, further interpretation is needed, often resulting in historically contextualising the moral proclamations so that you arrive at Covenantal moral relativism.
What happens when we morally interpret the biblical texts? Well, we use moral reasoning and moral intuition (and for which we do not need a god).
Where do we really derive our morality, then? Our own moral intuitions and moral reasoning. We apply these to the Bible; we do not derive them therefrom.
Now, I understand that sophisticated theologians™ claim that God underwrites objective morality and not necessarily that the Bible is the moral guide, but one would expect the actions of God and the inspired word of God to be reflective of that divine underwriting? Instead, the Christian has to mentally gerrymander to get out of the corners that the Bible often paints them into.
There is more moral clarity in the mind of the average human than in the pages of the Bible.