Gregory "the Great" and others continued to grapple with the contradictions and theological problems inherent within the belief in a personal Satan. Gregory especially developed the idea that Satan has power over humanity because God gave this to him in order to punish us for our sins. Again, this begs many questions. How can someone be punished for their sin by giving them into the hands of a being who wishes to make us sin yet more- and how can this be done by a God whose stated aim is to redeem humanity from sin? And why, then, did God supposedly have to buy us back from the Devil with the blood of His Son? And if this happened at the cross, then how is it that humanity is still under the power of "Satan" just as much after the crucifixion as before it? Seeing God has ultimate foreknowledge, why would He have allowed Satan to get away with all this? It seems to me that all this misses the point- God's heart is broken by our sin, by our freewill turning away from Him; and not because some rival god temporarily got the better of Him.
Anselm continued the tortuous arguments. Desperate to avoid accepting God as the author of evil, He continued to blame the Devil for it, but struggled with why God allowed the Devil to sin. Anselm claimed that God offered the Devil grace, but he refused it. And yet, given the ultimate foreknowledge of God, this again only drives the question of origins a stage further back- why did God allow that to happen, and from where did the Devil get the impulse to refuse grace?
Thomas Aquinas struggled with the origins of sin and evil by teaching that sin and evil are only in action, and therefore God wasn't the source of sin by providing freewill to people. Whilst it is the human mind which exercising God-given freewill which is indeed the Biblical source of sin, Aquinas' zeal to distance God from anything negative led him to deny the ABC of Christ's teaching in the Sermon on the Mount (Mt. 5-7). For there, clearly enough, the whole manifesto of Jesus was based around the theme that sin does not only occur in actions but also in thoughts. Again, Aquinas followed the usual Christian tendency to ignore the huge Biblical emphasis upon sin occurring in the heart, and therefore the need for mind control rather than merely cheering on God's side in some cosmic conflict which we observe from earth.