Throughout their mortal life, every soul is connected to a personal sin and virtue that grow according to how the person in question lives their life. Every time the soul does something good, or more specifically something rooted in the seven great virtues, their personal virtue gets stronger. Likewise, whenever they do something rooted in the seven great sins, their own sin is strengthened.
Upon death the personal sin and virtue are weighed against eachother, and whicever one is strongest overtakes and demolishes the other. If the virtue wins out, the soul is sent to Heaven where they'll awaken in their personal paradise. If the sin is stronger, the soul is sent to Hell where they'll be confined within a personal hell.