The idea that suffering is what God demands from us in order to "repay" Him our debts for sin, that is a portrait of an angry and insulted God, which is alien to Eastern Christianity.
This notion is a bit skewed. I have never been taught that God demands suffering. Rather, it is the concept of an individual 'offering' suffering up for their own transgressions or those of others.
"I have never been taught that God demands suffering. Rather, it is the concept of an individual 'offering' suffering up for their own transgressions or those of others."
To the extent that one can "offer up" personal, un-sought out suffering in an effort to become more like God, I suppose this is OK. But for Orthodoxy, this isn't any kind of atonement idea. We repent of our sins and pray for those who are evil to us because those are ways in which we become more like God. Some Orthodox writers posit that at the Final Judgment it is not our sins or even our good deeds which are weighed out in the balance, but rather how much we have become like Christ during our lives. This is because, to paraphrase +Athanasius in De Incarnatione, "God became man so that man could become like God."
The whole concept of Purgatory is based precisely on the idea that God demands punishment to His "satisfaction." This notion is driven by the somewhat pagan understanding of God's Justice -- one that is driven by Necessity to which even God is not immune. It implies that those who end in hell are there because of God.
God is Love, and Love is merciful and compassionate -- to the righteous and the unrighteous. If God were kind to some and unkind to others, God couldn't be unchanging and eternally the same.
The iniquities of mankind are forgiven through repentance. Those who do not repent in this lifetime cannot be saved. God applies the same expectations on us. Remember, unless we forgive we cannot be forgiven. And if someone repents, we must forgive (Luke 17:3-4).