In Anselm’s Cur Deus Homo, he divides the work into two short books. The first book contains objections raised by unbelievers because of their view that the faith is unreasonable, and responses by Anselm to their objections. The second book contains the purpose for which man was created and accentuates that its realization can only be obtained in the God/Man.
Responding To the Contemporary Critics: “It’s Dishonoring to God”
Book One: Responding to the Objections Raised by Infidels. This work begins with Boso (the one asking the questions) raising the objection that “we do injustice and bring dishonor to God…” when we claim that Jesus was born of a virgin, needed the nourishment of men to grow, grew tired and fatigued, and last of which was crucified among thieves.
Anselm’s response: we neither dishonor nor bring upon God any injustice by those things we claim, but instead we do praise and proclaim the inexpressible height of his mercy. Through the incarnation, God does more deeply demonstrate his mercy and love toward us, for, as by one man’s disobedience death reigns, so also by one man’s obedience life should be restored. Moreover, as sin had its cause in woman, so also it was fitting that through woman the author of righteousness be born from her, and in the same way the devil conquered the first Adam by the eating of the tree, so also the last Adam vanquished Satan by his suffering on the tree. Again, Anselm explains that redemption could not have been realized through any other being other than God (whether angelic or human) because if any other being should rescue man from eternal death, man would rightly have to be that redeemers servant. The problem however is that both angels and man were designed to serve only God through eternity.
“The Incarnation Seems Inconsistent with Reason”
Another objection raised against the incarnation by Boso is that it seems inconsistent with reason for the Almighty to “stoop to things so lowly, that the Almighty should do a thing with such toil”.
Anselm responds by accentuating that God’s will ought to be sufficient reason for whatever he does because his will is never irrational, regardless of our inability to understand. Furthermore, to think that it is unreasonable for the Almighty to stoop so low and embrace so much toil is to misunderstand our faith. For we assert that the Divine nature is indubitably impassible, He cannot be un-exalted, nor does he toil in anything He desires to effect. Moreover, the Lord Jesus Christ is very God and very man, one person who has two natures. Hence, when we speak of God enduring humiliation or suffering, it only refers to the feeble human constitution, which Jesus assumed. In the incarnation, there is no debasing of the Deity, but rather there is the exaltation of man’s nature.
“Why Should the Most Just Man be Punished for the Guilty?”
Something that also seems unjust and lacking wisdom for Boso is that the most just man should be punished for the guilty. Not only does God deserve condemnation for such an act, but this also argues against his omnipotence and justice.
Anselm responds by asserting that God neither put the innocent to death for the guilty, nor impelled Jesus to die and suffer against his own will for man’s salvation. Instead, Jesus willingly laid down his life.
Boso objects by citing many texts that demonstrate Jesus’ submission to the will of the Father, and as such, that this act was one of obedience to the Father’s will, not Jesus own free will. Anselm clarifies the misunderstanding between doing something at the demand of obedience as opposed to what he suffered because of his perfect obedience. For every rational being owes the demanded obedience to God and the Father claimed it from Jesus (in his humanity).
It would be unjust for God to demand death of a sinless man for whom God created to be happy in Him. Furthermore, it would not be right for God to make miserable by death a creature who is without fault, for that is not the goal of his creation. Rather than being compelled by God to die, Christ suffered death of his own accord, and by yielding up his life, Jesus is not offering an act of obedience, but rather on account of obedience in maintaining his holiness, he met death.
And when a scripture like “God did not spare his own son, but gave him up for us all”, it simply means that God did not rescue him, not that he sent him to die.
“Sin’s Meaning & It’s Relatedness to Satisfaction”
Now concerning the meaning of sin and how satisfaction for sin is realized, Anselm first explains that sin is not rendering to God his due. The debt man owes to God is to be subject to His will. By neglecting the aforesaid, man robs God and dishonors Him, thus sinning. To make satisfaction for the offence and be cleared of fault, a repayment of honor to God must be made in return. This is a debt every sinner must settle, yet is unable to repay on his own. Anselm continues the theme by pointing out that God would be unjust not to punish the unjust for their sin. For by not executing his justice, God would then not differentiate between the guilty and the innocent, and this is unbecoming of Him.
Anselm also deals with how God’s honor exists in the punishment of the wicked, how man cannot be redeemed without satisfaction for his sins being made, and how Jesus the God/Man necessarily realized the rescue for mankind. Moreover, how it’s impossible for the devil to be saved and how great God’s compassion really is.
 St. Anselm, “Cur Deus Homo,” Basic Writings, (Translated by S. N. Deane, Pp.191-302, © 1962 by Open Court Publishing Company, 2001 Printing).