Gustaf Aulén believes the 'classic' view of the atonement is only 'an idea, a motif, a theme' and not a 'theory'. 'It has been fully definite and unambiguous' in its expression, but 'it has never been shaped into a rational theory' (p. 157, Christus Victor).
The classic type is characterised by a whole series of contrasts of opposites, which defy rational systematisation, while the other two find rational solutions of the antinomies along theological or psychological lines.
...the oppositions of the classic type...are present wherever the classic type appears. God is at once the all-ruler, and engaged in conflict with the powers of evil. These powers are evil powers, and at the same time executants of God's judgment on sin. God is at the same time the Reconciler and the Reconciled. His is the Love and His the Wrath. The Love prevails over the Wrath, and yet Love's condemnation of sin is absolute. The Love is infinite and unfathomable, acting contra rationem et legem [contrary to reason and law], justifying men without any satisfaction of the Divine justice or any consideration of human merit; yet at the same time God's claim on men is sharpened to the uttermost.
Every attempt to force this conception into a purely rational scheme is bound to fail; it could only succeed by robbing it of its religious depth. For theology lives and has its being in these combinations of seemingly incompatible opposites.
(p. 155, Christus Victor)
In this respect he is a typical Lutheran. Frustrating to a rationalist like me and yet full of life and colour.
He calls on Luther to aid him in his cause, and even though I think Luther was less opposed to substitutionary atonement than Aulén believes, it is difficult to argue that Luther was ever systematic. He wrote scores of volumes of work and yet almost nothing that could be described as systematic.
More recently I have encountered much of this anti-systematic Lutheranism in Gerhard Forde and Oswald Bayer. Steven Paulson, a student of Forde, recalls another theologian quip about Forde that he had "lost interest in doing systematic theology".
Another student of Forde, Mark Mattes's has recently written a book analysing the theology of Jungel, Pannenberg, Moltmann, Jenson and Bayer. He argues:
Theology should not be about providing an overall system, but instead should deconstruct systems. Undoubtedly, it is desirable for the church's catechesis to seek rhetorically a structured presentation of the faith ...[but not] a "God's eye view" of all reality...The most important task in theology is not construction but discernment. All construction needs to subordinate itself to this discernment, and not vice versa.
(pp. 181-182, The Role of Justification in Contemporary Theology)
Against this background it is only really Bayer that he finds limiting theology appropriately:
For Bayer, theology is not done to integrate all knowledge, either theoretical or practical, into an abstract unity, but to limit reason to its proper fields. It is the art of discerning what God is saying to us, not peering into the divine
(p. 149)
In biblical theology I have found Seifrid also upholding this lack of systematisation.
PS In case you wondered, I feel the Lutherans have something useful to say here, but I am not totally with them.