How do you recognize the work of God in your life?  Is it in the form of a crumbling life that you are encouraged to rebuild through faith?  Is it returning lies and misdeeds with truth and love because it's how God commands us to deal with our enemies?  Even the pagan nations around Jerusalem recognized that God must be causing the work to be done for it was not possible though man alone.  The rebuilding of the walls was a physical means to a spiritual end.  They were intended to bring allegiance back to Him, a reminder to all of His Sovereignty.