The wicked man is a punishment to himself, but the upright man is a grace to himself—and to either, whether good or bad, the reward of his deeds is paid in his own person.
~ St. Ambrose of Milan, De Officiis 1.12
This perspective of St. Ambrose of Milan is one that is quite common among ancient Christians. In some sense they also expect a coming, final judgment, of course, but I am not clear that such was any different than the natural consequences of our actions now, simply taken to their logical ends. In any case, many today, perhaps, could benefit from reconsidering their concepts of sin, merit, reward, and punishment from this more anthropological perspective of St. Ambrose.
Another common, and related, concept is that of evil being not, properly speaking, a thing at all but a corruption of goodness. St. Augustine is perhaps most famous for this formulation, but it is not limited to him. The idea is actually quite simple: as light is to darkness, as heat is to cold, so good is to evil.
Human beings, to get back to St. Ambrose, have an innate capacity for virtue as icons of God. The extent, however, that the likeness of the divine image is displayed through us is conditional upon the likeness of our character to God’s. According to St. Gregory of Nyssa, in fact, “Christianity is an imitation of the divine nature.” The goal of Christianity, on his account, is to be what human beings are meant to be. This, perhaps, accounts for the often universal wisdom that can be gleaned from the Christian spiritual tradition. Much of what the desert fathers say can be found among Zen Buddhists, for example, with the important exception that for the former spiritual peace is rooted in communion with Jesus Christ.
In any case, the anthropological point is that if evil is a distortion or privation of goodness, then to do evil and be evil is to diminish something good within us. On the other hand, to do and be good is to grow something good within us. And virtue is its own reward: it is the source of true joy. Vice, on the other hand, torments us: it is its own punishment.
As the Rule of Saint Ciarán puts it: “Heaven is the reward of the person who, for the sake of all people, disciplines his [or her] own heart.” And C. S. Lewis puts the following into the mouth of George MacDonald in The Great Divorce: “at the end of all things … the Blessed will say, ‘We have never lived anywhere except in Heaven,’ and the Lost, ‘We were always in Hell.’ And both will speak truly.” Furthermore, lest I forget the most important, Christ himself declares, “The kingdom of God does not come with observation; nor will they say, ‘See here!’ or ‘See there!’ For indeed, the kingdom of God is within you” (Luke 17:20-21).
Whatever the case when it comes to the accounting of our deeds on the dreaded day of judgment, it is far more important right now to realize how virtue and vice affect us every day. Vice pushes us from passion to passion, and the more we set our desires on those things which fade away, the more clouded our vision of the eternal becomes, pushing people quite literally to madness, even a foretaste of hell itself. Virtue, on the other hand, is health to the soul, and far more: it is the presence of divine grace to those who possess it, a heavenly treasure that does not pass away, and indeed, a foretaste of heaven itself, if only we take the time and learn the discipline necessary to cultivate it in our hearts.