The bible is like a conversation about God. All the authors of the OT believed Israel had been given a special vocation by their god Yahweh, but they understood that calling in different ways. So for example, Proverbs tells us if we keep god's laws we will be blessed, Job tells us this is not always true, they worship the same god but have contrasting theologies.
The NT tells us Jesus is the final point of the conversation. The purpose of the bible is to point to him and it can then be read back through him, and that is how we understand the conversation and which parts should be affirmed.
Just my 2 pence. :)