Why is God's Judgment only Heaven or Hell?

I know very little of the Christian Faith or of any other faith for that matter, but this question struck me as relevant maybe not just to Christianity but also to all faiths as a whole. Penal systems on the Earth are there to create order in society and breaking the laws under a particular system have "degrees of penalty" such as a bank robber would be given 10 years in prison whereas an adolescent who stole from a gumball machine outside the local store would only be given a slap on the wrist and told not to do it again. In both these cases the crime was theft but they are not judged equally. So why is God's judgment of man so extreme: either man gets eternal bliss or eternal pain? Why does even the *slightest* transgression of God's law is punished the same as a *greater* transgression?