Claiming that imputation is based on legal union may sound rhetorically convincing, but it logically boils down to saying that imputation is based on a relationship in which it is right and appropriate that the status of one person, whether righteous or sinful, is imputed to another. “And what is the nature of that union?” Well, it is a union that involves imputation!
The entire statement is incredibly narrow and circular.
Keep in mind that imputation is supposed to actually explain something–how a holy God can justly grant pardon to sinners and accept them as righteous in his sight. Even people who think they are simply expounding what the Bible says, usually spend a great deal of time setting up a theodicy-dillemma: If God is altogether perfect then how can he overlook sin? The whole point is to appeal to justice to show that God must not forgive arbitrarily.
Imputation is supposed to answer this dilemma. But claiming that God simply counts one person’s obedience, suffering, and death as the fulfillment of the his righteous requirements of a multitude of sinners, is just as arbitrary and unjust. If God can just pretend that we are righteous with Christ’s righteousness (if imputation is just God doing math in his head) then how is that not just as arbitrary and unjust as simply forgiving them in the first place, without demanding anything from Jesus or anyone else to provide a “basis” for it? Imputaton, rather than explaining the basis, becomes a way of saying no basis is necessary.
Of course, if this was what the Bible presented to us, we would be required to accept it. We would be required to be satisfied with this answer and simply admit that it does not appear adequate to many people, including those who try to justify the doctrine as a vindication of how God can justly forgive sinners.
But in fact, the Reformation never taught this version of imputation. Both in the case of Adam and in the case of Christ, imputation was grounded in union. This eventually got obscured in some nominalistic strains of the Reformed Tradition so that the traditional view had to be defended in the nineteenth century.
Whether or not this settles all arguments with possible accusations against God’s justice is impossible to say. What I do know is that it is what the Bible teaches, as is witnessed by the Reformed heritage, and thus it is the final word God has given in his own defense of his just, gracious, and non-arbitrary character. If He is satisfied with it than Christians should be satisfied with it as well.
We are conceived as sinners because we all come from Adam and are born in Adam by an organic unity. We receive the imputed righteousness of Christ by faith because we receive Christ by faith and, being clothed in Christ, are clothed in his righteousness.
All nominalistic versions if imputation whereby it becomes a mental operation in God’s mind will lead to hypercalvinism and (since we tend to image the god we worship) unconfessional definitions of “faith” which make it nothing more than a convert doing math in his head.
The Reformed Faith is richer than this, more Biblical than this; and if that were not so, then it would be a minor deviancy in Christian history rather than a true apostolic witness in the power of the Holy Spirit.
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