When I eat something good it lasts for only a short time and it is gone. In heaven I am face to face with God. I enjoy God himself. God is infinite so that enjoyment lasts an infinite 'amount of time' (time and heaven is a topic for later). The choice of choosing God is ultimately an infinite choice. I cannot enter into heaven for part of time since heaven is an infinite experience. I can ultimately either accept or reject heaven, there is no middle ground. Everyone in purgatory will eventually enter heaven. Purgatory has time. Heaven actually is an existence beyond time. So heaven is an infinite decision. If I accept heaven I will always be in heaven. If I reject heaven, I reject it forever. Once I am in heaven I have no desire to leave, or to sin since I will recognise that total ugliness and stupidity of sin. Heaven satisfies more than my every desire.