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Cur Deus Homo

Cur Deus Homo ("Why God was a Man") was written from 1095 to 1098 once Anselm was already archbishop of Canterbury as a response for requests to discuss the Incarnation. It takes the form of a dialogue between Anselm and Boso, one of his students. Its core is a purely rational argument for the necessity of the Christian mystery of atonement, the belief that Jesus's crucifixion was necessary to atone for mankind's sin. Anselm argues that, owing to the Fall and mankind's fallen nature ever since, humanity has offended God. Divine justice demands restitution for sin but human beings are incapable of providing it, as all the actions of men are already obligated to the furtherance of God's glory. Further, God's infinite justice demands infinite restitution for the impairment of his infinite dignity. The enormity of the offence led Anselm to reject personal acts of atonement, even Peter Damian 's flagellation, as inadequate and ultimately vain. Instead, full recompense could only be made by God, which His infinite mercy inclines Him to provide. Atonement for humanity, however, could only be made through the figure of Jesus, as a sinless being both fully divine and fully human. Taking it upon himself to offer his own life on our behalf, his crucifixion accrues infinite worth, more than redeeming mankind and permitting it to enjoy a just will in accord with its intended nature. This interpretation is notable for permitting divine justice and mercy to be entirely compatible and has exercised immense influence over church doctrine, largely supplanting the earlier theory developed by Origen and Gregory of Nyssa that had focused primarily on Satan 's power over fallen man. Cur Deus Homo is often accounted Anselm's greatest work, but the legalist and amoral nature of the argument, along with its neglect of the individuals actually being redeemed, has been criticized both by comparison with the treatment by Abelard and for its subsequent development in Protestant theology.