An old Christian summary of the evil forces with which we have to contend calls them "the world, the flesh and the devil." Each term of this unholy triad needs defining. To take first "the flesh," this is not the body. Happily, most Christians have now shed the old Platonic prejudice that the material is more susceptible to evil than the intellectual or the spiritual. "The flesh" should be understood in Paul's sense, as a deeply rooted tendency to evil within our human nature as we experience it. While "the flesh" identifies a root of evil within the individual, "the world" identifies human society as a source of evil. Society is more than the sum of individuals. It is a school of evil in which we are all educated, a reservoir of evil to which we all contribute, a web of evil in which we are all entangled. Of course, it is no more wholly evil than is the individual. But just as society can nourish the good in an individual and make more of it than it could be in itself, so society can recruit people for atrocities of which the mere individual would not have been capable.  

Finally, "the devil" names a source of evil beyond the human. Though this term personifies superhuman evil, we should not insist too much on a "personal devil." Personhood is good; evil diminishes and destroys it. If we think of the devil as some kind of anthropomorphic creature, capable of relationships and moral choices, we begin to ask inappropriate questions, like the old theological puzzle: why can the devil not be saved? The devil cannot be saved because there is nothing for God to save. Unambiguous evil, a blind will to spoil and to destroy, God can only destroy. That there is such a will, an influence for evil which cannot be reduced to human tendencies to evil, individual or corporate, is debatable in a way that the latter are not. Most of the Old Testament manages without such a concept. But the New Testament finds it necessary. Its most useful function is that it keeps us from underestimating evil.  

By recognizing the unholy triad, we can recognize the complexity of evil. These three sources of evil combine and collude in many ways. For example, in a highly oppressive political, social or economic system, there are usually some real villains, but most members of the exploiting class are not more personally wicked than the human average. They do not really want to be the source of the suffering the system causes to others and often try to avoid admitting to themselves that they are. But nor are they purely passive victims of the system. It has them in its grip only because it has an ally within their own hearts. A kind of self-interest which in other contexts would be less damaging (though never negligible) here supports a very evil system. But there are other cases where an excess of evil cannot easily be attributed to society. A person can so nourish their own evil inclination as to become unusually intent on evil. The nourishment comes from society, but is no more available to them than to others. These are just two of many different possibilities which we must not reduce to a simplistic single model of how individual, social and demonic evil interact. 

There are many false ways of dealing with evil. One is to explain it. There are armchair theodicies which explain why there has to be evil so that greater good may come from it. There are non-religious equivalents which treat evil as, for example, a necessary stage in the evolutionary process. Such explanations take the evil out of evil by justifying it. They reduce our moral outrage at it and sap the will to resist and to overcome it. Evil is what should not be. If we explain why it must be we mask its true nature as evil.  

Another false way of dealing with evil is to subsume it into a greater whole which encompasses good and evil. There is a currently fashionable polemic against the "dualisms" of the western religious tradition. This argument misleadingly correlates a whole series of different kinds of dualism (God and the world, good and evil, spirit and matter, male and female etc.) as though a preference for wholeness can supersede them all. With regard to the dualism of good and evil, this relates to a Jungian psychology which seeks wholeness through the integration of the dark side of our nature, and finds the model for this in an image of God which has a dark as well as a light side. But this is another way of legitimating evil, suppressing the basic moral perception of evil as what should not be. There is nothing beyond good and evil; but there is the God who, being absolute goodness, must overcome all evil. Wholeness is achieved not by incorporating but by renouncing and resisting evil

We cannot deal with evil by explaining it (since it is the inexplicable surd in reality) or by integrating it (since it is inherently destructive). So long as we recognize evil as truly evil, it is obvious that evil must be overcome by goodness. Since we are morally ambiguous creatures, susceptible to evil, ultimately only God's unassailable goodness can overcome evil. But so that he can redeem us from evil, rather than destroying us as evil, he makes his goodness available to us as the source of our power to resist evil. Since there is a root of evil within each of us, this resistance is painful. We must die to self daily. Since evil transcends the individual, resistance to it must do so too. We must be salt in the soil of the earth and light in the darkness of the world. And since evil transcends the human, resistance to it requires the whole armour of God.