Aulen's book is short and its structure is a classification. He proposed that the Western discussion of the atonement had been running on an inadequate map, one with only two positions on it, the objective and the subjective, meaning Anselm and Abelard. On that map every account either changes something outside the human being or changes something inside one, and the whole argument becomes a choice between them.
Aulen argued for a third, which he called the classic or dramatic idea and which he held to be older than both. In it God is the actor throughout. God is not the object that receives a payment and not merely the exhibitor of a display; God in Christ enters the field, is subjected to death, and defeats the powers that held humanity, so that the atonement is continuous with the incarnation at one end and the resurrection at the other. The reconciliation is real and objective, as in the Latin type, but it is achieved by conflict rather than by satisfaction.
Two further claims did most of the work in his argument. The first was that this dramatic idea was the characteristic view of the early church, obscured but not extinguished afterwards. The second was that Luther held it, and that the Lutheran scholasticism which followed him did not, so that the Reformation itself had been misread on the point.
Whatever one makes of those claims, they had an effect that is not in dispute. Before 1931 an English-speaking theological student met the patristic material, if at all, as a set of curiosities superseded by Anselm. Afterwards it was a position with a name, a case and a bibliography. The phrase Christus Victor entered the general vocabulary and is now used by writers who have never read the book and who would reject parts of it.