Evil in its lexical opposition to good does not exhaust the complexity of its meanings. As opposed to the conventional well, it can be understood as the non-desirable as such.
In this conception of evil in bodily or psychic sense, associated in philosophy at least a metaphysical meaning and a moral one. Another much greater theoretical thickness.
The metaphysical evil is transformed, according to Augustine, in a moral evil due to an error of the human will: this chooses to direct the man towards something, a particular commodity traded to the supreme Good which is God alone.
In fact every being is good, because it was created by God. There cannot be a principle of evil in contrast to that of good and struggling with it, because no absolute principle, as such, as it tolerates the presence of another principle equally absolute, otherwise it would just total and absolute, but relative.
Similarly it is possible that the evil finds its reason for being in God. In his moral choices, however, the man, while being guided by love, also has a free will. He has the opportunity to choose between two alternatives substantially freely: when you drive by true love, the man always chooses the supreme Good, because, enlightened by the light of God, he learns to value the assets according to their actual minor hierarchy. When it is driven by an altered love, he is led to desire a type of inferior good, like wealth or greed, which he is treated and considered as superior goods. Therein lays the possibility of moral evil.
Augustine did not negate the suffering or sin, in the Christian sense. Physical evil, on the one hand, is a consequence of moral evil, since it springs from the same source metaphysical, ontological, or by a non-being. On the other hand, however, it has for Augustine also a positive meaning, Transmuting sometimes into an instrument capable of leading to the faith for inscrutable ways. In this way Augustine overcomes a widespread belief in the previous period, which conceived of the disease and the pain only as a sort of divine punishment of human actions.
Physical evil is the same that even Christ had to suffer for our atonement, during the Passion and martyrdom on the cross, while being Almighty: He did not oppose you to leave leeway to the human will.
Here then the problem of evil is connected with that of human freedom. If man were not free, he would not deserve, nor guilt. The dilemma that arises with this claim is whether there is free will or predestination, problem that has arisen as a result of original sin.
God, who is omniscient and knows the future, gave full freedom to man, but he knows that, leaving him free, these sin. God could also intervene to stop him, but he does not interfere with his free will.
The man, as sinning, committed the original sin, which has compromised their freedom, turning it against itself. Although he has become unworthy to receive salvation, God, knowing his choices to evil or to good, gives to some, with the Grace, the ability to save themselves, while others leave the freedom of being damned; However, this is not an arbitrary divine choice, but it's just to the foreknowledge of God, eternity (that is, beyond the time), he sees those who can receive the Grace and those who cannot. The latter even if they received not only not would be saved, but would fall even more.
For Augustine, therefore, not the will of God would be just ahead of the will of man, because that our will is the only one that really makes us deserving of salvation or damnation; In fact, even if no man could be saved with just their will, those who could be saved are rescued by divine grace, which helps them in their preparation.
Paul of Tarsus
Christ responds to his disciples, who had asked him: "Who then can be saved?". Jesus looked upon them up and said: "This is impossible for men, but with God all things are possible." (Mt 19,25-26)
It would, moreover, impossible to investigate the reasons why God intervenes in favor of some and not others, because we have no right to criticize God.
Augustine refers in regard to the words of Paul of Tarsus: "O man, who are you to argue with God? Shall the thing formed say to him who formed vase of him:" Why did you make me like this? ". Maybe the potter who is clay master, do with the same lump one vessel unto honor and another for dishonor?"
Foundation of human freedom is therefore for Augustine divine grace, because only with the grace man becomes able to execute our own moral choices. It must be distinguished in this respect the free will, which is the desire to choose in principle between good and evil, freedom, which is rather the will to put these decisions into practice. Here you will activate the controversy of the last years of Augustine against Pelagius: since man is corrupted by original sin of Adam, and then perhaps well-intentioned but easy prey to evil temptations, God not only intervenes to enlighten man on what it is good, but also to infuse the actual will to pursue it.