St. Augustine in Confessions writes in Book I, Chapter 20:
"For my sin was in this -- that I looked for pleasures, exaltations, truths not in God Himself but in His creatures (myself and the rest), and so I fell stright into sorrows, confusions, and mistakes."
It seems that for Augustine sin is not the breaking of some rule, but something that leads us away from our true happiness. The punishment of sin is really the consequence of the very nature of what makes something a sin.
Thoughts?