Evil isn't an absence of God -- rather, it's our voluntary rejection of Him. The following is taken from http://www.fatheralexander.org/booklets/english/beatitudes.htm by Fr. Seraphim Slobodskoy. I think it could probably use a bit of editing, but I'm reproducing it unchanged ....
The concept of evil in the world imposes a grave burden of doubt in the hearts of many faithful people. It seems inconceivable that God would permit evil. In fact, God in His Omnipotence could easily eliminate evil. How could a merciful God allow the evil deed of a single offender to doom thousands, sometimes millions, or even half of humanity to poverty, grief or disaster? What then is the meaning of evil? With God nothing is without reason. In order to answer this question, it is necessary to recall what evil is.
By the term evil we do not mean suffering, need and deprivation, but sin and moral guilt. God does not desire evil. Almighty God cannot approve of evil. More than that, God forbids evil. God punishes evil. Evil or sin is in contradiction to the will of God.
Sin began, as we know, when the highest angel, created by God, insolently
rejected obedience to the blessed will of God and became the Devil. Evil
is caused by the Devil. He inspires or influences the occurrence of sin
It is not the body which is the source of sin, as many believe. The body becomes an instrument of sin or of good not of itself but through the will of a person. True faith in Christ elucidates the following two causes of sin in the world:
The first cause lies in the free will of man. Our free will is the mark of our likeness to God. This gift of God elevates mankind to the highest of all earthly creatures. By freely choosing good and rejecting evil man exalts God, glorifies Him and perfects himself.
In the book of the Wisdom of Sirach (Ecclesiasticus 15:14), it says, He (God) in the beginning made man and left him in the hand of his own free will.
By this God gives to people of good will the possibility to attain Heaven, and to people of evil will, the other world. However it happens, the result is only by means of a person's free will.
Saint Cyril of Jerusalem says, "If nature were fused together and it were not possible to do good by free will, then for whom would God prepare the inexplicable crown? Sheep are gentle, but they will never be crowned for their gentleness, because their gentleness comes not from their own free will but from their very nature."
Saint Basil the Great says, "Why is not sinlessness incorporated our nature, so that it would be impossible to sin, even if we wanted? You do not recognize good and faithful servants when you keep them restricted, but only when you see that they voluntarily fulfill their responsibilities before you. Virtue comes on the condition of free will, not necessity; and free will depends on the condition that we be free. Therefore, whoever reproaches the Creator for not creating us sinless prefers the irrational, immovable nature, not having any yearnings, nature gifted with judgment and independence." In other words, he prefers robots to intelligent creatures.
Thus, the internal cause for the origin of evil, or sin, consists of the will of man.
The second basis for the existence of evil consists in the fact that directs evil to good. But God does not tolerate evil for the sake of good. For God, it is not necessary to pay such a high price.
God does not wish for evil under any circumstances. But when evil penetrated into the world through the fault of sinful people, then God, in plan for the world, compelled even evil to serve good. For example, the sons of Jacob sold his brother Joseph into slavery. They committed an evil deed, but God turned the evil into good. Joseph rose in Egypt and acquired the capacity to save from starvation the family from which the Messiah would come. When Joseph saw his brothers several years later, he said to them, "You intended evil against me, but God turned it into good!"
In the days of the Apostles, the Jews persecuted Christians in Palestine. The Christians had to flee from Judea, the land sanctified by the life and blood of the Saviour. But everywhere they went they sowed the words of the Gospel. The sins of the persecutors were directed into spreading Christianity.
The pagan emperors of Rome persecuted the young Christian Church. Tens of thousands of martyrs shed their blood for Christ. The blood of the martyrs became seeds for millions of new Christians. The fury of the persecutors, their sins of hatred and murder were directed by God in this instance into the building up of the Church. They thought and accomplished evil. God turned all of their deeds to the good. The history of mankind, right up to the events of our day, testifies to the truth of these words. The greatest downfall of man concurred with the greatest religious triumph, the turning of men to God.
We need only have patience and wait, one day is with the Lord as a thousand years, and a thousand years as one day (2 Peter 3:8).
But this intertwining of evil into the plan for the management of
the world did not appear to be some sort of belated addition for the correction
of creation. The intertwining of evil was provided for in the act of the
eternal will of God, in which was determined the creation of the world.
For God is the eternal today! His foresight extends to eternity. It functions
always and without interruption. (Extracted from a brochure by L. Lusin,
"Who is Right?" with additions.)
For inquirers.... the Wisdom of Sirach is a part of the Septuagint -- the Greek language Old Testament which was prevalent at the time of the Lord and the Apostles.
The River of Fire by Kalomiros, mentioned above, is (in my opinion) usually best read in conjunction with a discussion group... even if the group is only two people. Heavy stuff... and can be found at http://www.orthodoxpress.org/parish/river_of_fire.htm.