Some partial, exploratory, perhaps incoherent thoughts on imputation.
1) A recurrent charge against imputation is that it seems to rest on a legal fiction - someone being treated as guilty who’s not, someone being treated as just who’s not.
2) There are hints within the Levitical system that imputation is not just a strange exception to the standard way of doing things, but that some act of imputation is always at work in any sinful action.
3) I have in mind the phrases “he shall bear his iniquity” and “their/his blood on them/him.” These phrases occur in contexts prescribing capital punishment for various crimes. When the text adds “his blood is on him,” the implication is that the blood is not on the people who shed the blood - namely, the citizens who stoned the criminal. But the further implication is that the blood must be on someone . Free-floating blood, as it were, is not an option. Either the person who did the crime must bear responsibility, or the people who failed to carry out the crime, or, in some cases, a substitutionary animal must bear responsibility for the crime. That is, some assignment of responsibility is necessary.
4) That seems to presume that there is some distinction between the act itself and the assignment of responsibility for the act. When a man takes his sister as a wife, he is “cut off in the sight of the sons” of Israel (Lev 20:17). That probably does not refer to a death penalty. In any case, that is followed by the declaration that he “bears his guilt.” But if the wrong action attracted guilt to it “immediately,” then the additional statement that he bears his guilt is redundant. Of course he bears his guilt; who else would? But the phrase suggests that someone else might , and thus suggests that the assignment of responsiblity or guilt is a distinct “event” from the wrong action itself. In short, wrong acts must be judged wrong.
5) There’s a particular spin on this for capital crimes. A man, for instance, has homosexual relations in ancient Israel, and by the Torah must die (Lev 20:13). He has committed a wrong, and must be punished. But the punishment itself needs to be atoned. His death leaves the land bloodstained. That can’t be left alone. Somebody has to pay for it. The law says that the person who died paid for it with his death. His death is a punishment for the crime, and the bloodshed involved in his death is assigned as his responsibility. In a sense, there’s a kind of inverted double jeopardy here - the man dies once for two different wrongs - the wrong of his original sodomy and the wrong of shedding blood on the land. The Torah treats his bloodshed as if it were suicide - “his blood is on him.”
6) If there’s always an assignment of responsibility distinct from the wrong of the act itself, then that leaves open the possiblity (#4) that someone other than the actor might bear that responsibility. It suggests the possibility that the iniquity might be “imputed” to another, to a sin-bearer. On this theory, “imputation” is not what happens when someone else takes the guilt; imputation is necessary for any assignment of guilt, whether to the perpetrator or to someone else.
7) This rests on a social understanding of human being. Let’s start at the other end, with a pure individualistic account. On individualist premises, if I act badly, I’m guilty. My guilt is simply mine; no one had to judge me guilty; no one had to assign responsibility. My guilt is mine just as completely and immediately as the action itself.
On the theory I’m offering, guilt and responsibility are assigned socially/theologically, that is, by another or Another. Responsibility is mine only when it is assigned to me, and it might not be, for various reasons (such as the incarnate Son agreed that it be assigned to him). I am guilty or innocent in the regard of the proper judge/Judge.
8) On this suggested view, there is no “open space” for the legal fiction to occupy. There’s no “real inherent guilt” that is cancelled or ignored in favor of an “imputed righteousness.” I am either guilty or not by virtue of God’s assignment of responsibility, guilt, or innocence. That simply is my guilt or innocence, rather than something added to the “inherent” guilt or innocence of my action. If He says I’m righteous, there you go. It’s over. If He says that He’s taking responsibility for my sin, it’s over.