On What Basis Is That Judgment Made?

There is no moral basis for moral obligation unless we argue that nature is in some part unnatural.  We can’t know that nature is broken in some way unless there is some supernatural standard of normalcy apart from nature by which we can judge right and wrong.  That means there would have to be a heaven or God or some kind of divine order outside of nature in order to make that judgment.

– Tim Keller, Reason for God: Belief in an Age of Skepticism, copyright 2008, page 157-158