Rick at Light from Light blog has a good article, titled "The Divine Service and Begging."
He quotes from Dr John Kleinig in Grace Upon Grace: Spirituality for Today:
Because our spiritual life and health depends on receiving from Christ, we exercise our faith by becoming beggars before God. And that’s not easy for us who fancy that we are producers of spiritual goods and owners of spiritual gifts. The place to begin learning to receive is our regular involvement in the Divine Service. The classical order for the Service of Word and Sacrament puts us and keeps us in the position of beggars before God. It invites us to join the company of holy beggars in four important places.