Anselm's treatise takes the form of a dialogue in which his interlocutor, Boso, presents the case of the infidels who object to the logic of the incarnation of God as Man. Anselm avails himself of reason to justify why God did this. Anselm justifies his use of reason, furthermore, by claiming that reason can be a spiritual practice. Therefore, according to Augustine, there is no reason why it would be inconsistent to use logic (or reason) in a discussion of God.

Anselm devotes a significant amount of the text to a discussion of sin itself. Sin is a debt (on the part either of man or angels) owed to God as a result of wickedness. Sin, according to Anselm, robs God of his honor. The practice of redeeming sins is thus an exercise of justice. Put another way, paying the debt of sins is required in a just kingdom (such as God's). If man had not sinned, he never would have died.

Atonement is famously the phenomenon whereby Jesus redeemed mankind before God. God made Jesus so that Jesus might delight in the enjoyment of God. It was also not only necessary but expedient that Jesus die for mankind's sins, as Jesus is the only figure who was both of the divine and of man.

For a sin to be atoned (and a debt repaid), the substance offered by way of atonement must be the same of that which was robbed (in the case of Jesus: divine honor). Moreover, the one performing the act must be akin to the one who committed the sin (man). Jesus alone satisfies both requirements, and so, according to Anselm, Jesus was the necessary and figure to accomplish this atonement.