What is biblical theology? It’s an attempt to get at the unstated assumptions from which the biblical authors make their statements. The only access we have to those assumptions are the statements they make. Take Leviticus, for instance. The book has all these instructions for offering all these sacrifices, but it never states the rationale for those sacrifices. At least, it never states that rationale the way people living over 3,000 years after the book was written in a vastly different culture would like to have the rationale stated. So from what the book does say, biblical theology attempts to get at the rationale that Moses, in this case, has for the instructions, and which the original audience of the book knew, making it unnecessary for him to spell it out.