James Buchanan: Justifying righteousness comes from imputation of Christ's perfect righteousness, not progressive infusions of righteousness

"This righteousness--being the merit of a work and not a mere quality of character--may become ours by being imputed to us, but cannot be communicated by being infused; and must ever continue to belong primarily and, in one important respect, exclusively to Him by whom alone that work was accomplished.

... "For the merit of one can never, in any case, become available for the benefit of others, except when it is imputed to them. It cannot, from the very nature of the case, become theirs by infusion. The merit of one may be reckoned or put down to the account of another; but how can the merit of any work be infused, as a personal property, as holiness may unquestionably be?

... "Most of the leading errors on the subject of Justification may be traced to obscure or defective views in regard to the nature or import of imputation, and have arisen from supposing either that it consists in the infusion of moral qualities, in which case Justification is confounded with Sanctification; or that, in so far as imputation may be distinguished from such infusion, it is founded, at least, on the moral qualities which thus become inherent, in which case Justification has for its immediate ground a personal and not a vicarious righteousness. … while the righteousness of Christ, considered as the merit of His Mediatorial work, may become ours by being imputed to us, it is not communicated as an inherent habit or quality might be … The whole merit is His; the gracious imputation of it only is ours.”

(Dr. James Buchanan, "The Immediate and Only Ground of Justification: The Imputed Righteousness of Christ")