Justice and grace. To my belief God allowed man to make his own decisions instead of forcing some sort of automotron love. Love cannot be forced or it is not love. Sin needed to be punished and according to the bible Hell is here because of a choice humans made not to follow the rules God gave. Heaven is not bribe, but a reconciliation with God through his sacrifice of his son who I believe was perfect and took on the sin of all. By believing that God did this and accepting it, he allows our many past sins and future sins to be washed away. That's not to say we can live as we wish and then at the end turn in some sort of get into heaven card.

I understand why it does not make sense to many people and there are many hypocritiacal christians who say one thing and do another. But to the best of my knowledge, I believe in my heart that heaven and hell are much deeper topics than merely a reward and a threat.