You asked me to expand on this…
I will try to present the view of the Reformers in as concise a way as I can… These doctrinal issues are getting to the doctrine of justification which I believe is at the very heart of the gospel (Romans 1:16-17)… And I would view as at the heart of the Protestant Reformation, which is why many on here might see this as one of the great heresies, and I would see it as one of the greatest doctrines of the gospel.
From my understanding, the doctrine of justification of the Roman Catholic Church is a doctrine of “infused righteousness;” [See The Canons and Decrees of the Council of Trent (1563), “Decree on Justification”. Ch. XVI] whereas the doctrine of justification of Reformed Protestantism is a doctrine of “imputed righteousness.”
From the Westminster Shorter Catechism, Question #33:
Q. 33. What is justification?
A. Justification is an act of God’s free grace, (Romans 3:24) wherein he pardoneth all our sins,(Romans 4:6-8; 2 Corinthians 5:19) and accepteth us as righteous in His sight,(2 Corinthians 5:21) only for the righteousness of Christ imputed to us,(Romans 4:6, 11; Romans 5:19) and received by faith alone. (Galatians 2:16; Philippians 3:9)
The Westminster Confession states the following:
Those whom God effectually calls, He also freely justifies;(Romans 8:30; Romans 3:24) not by infusing righteousness into them, but by pardoning their sins, and by accounting and accepting their persons as righteous; not for any thing wrought in them, or done by them, but for Christ’s sake alone; nor by imputing faith itself, the act of believing, or any other evangelical obedience to them, as their righteousness; but by imputing the obedience and satisfaction of Christ unto them,(Romans 4:5-8; 2 Corinthians 5:19, 21; Romans 3:22-28; Titus 3:5-7; Ephesians 1:7; Jeremiah 23:6; 1 Corinthians 1:30-31; Romans 5:17-19) they receiving and resting on Him and His righteousness by faith; which faith they have not of themselves, it is the gift of God.(Acts 10:44; Galatians 2:16; Philippians 3:9; Acts 13:38-39; Ephesians 2:7-8)
The Reformed theologian Louis Berkhof wrote as follows…
“Justification may be defined as that legal act of God by which He declares the sinner righteous on the basis of the perfect righteousness of Jesus Christ. It is not an act or process of renewal, such as regeneration, conversion, and sanctification, and does not affect the condition but the state of the sinner.” (Berkhof, Louis. Manual of Christian Doctrine (1933, reprinted 2002). 256-257.)
The French Protestant Reformer, John Calvin, wrote the following…
“On the contrary, justified by faith is he who, excluded from the righteousness of works, grasps the righteousness of Christ through faith, and clothed in it, appears in God’s sight not as a sinner but as a righteous man. Therefore, we explain justification simply as the acceptance with which God receives us into his favor as righteous men. And we say that it consists in the remission of sins and the imputation of Christ’s righteousness.” (Calvin, John. Institutes, Book III. Ch. XI. ii.)