Many Protestants wish to claim St. Augustine as a teacher of justification by the imputation of Christ’s righteousness. The following quote reveals that St. Augustine understood justification as the transformation and renewal of the soul, not merely as a forensic declaration or acquittal:

“For what else does the phrase ‘being justified’ signify than being made righteous, — by Him, of course, who justifies the ungodly man, that he may become a godly one instead? For if we were to express a certain fact by saying, ‘The men will be liberated,’ the phrase would of course be understood as asserting that the liberation would accrue to those who were men already; but if we were to say, The men will be created, we should certainly not be understood as asserting that the creation would happen to those who were already in existence, but that they became men by the creation itself…In like manner, we attach one meaning to the statement, ‘God sanctifies His saints,’ and another to the words, ‘Sanctified be Thy name; ‘ for in the former case we suppose the words to mean that He makes those to be saints who were not saints before, and in the latter, that the prayer would have that which is always holy in itself be also regarded as holy by men, — in a word, be feared with a hallowed awe.”

– St. Augustine, On the Spirit and the Letter, 26:45 (A.D. 412)

St. Augustine clarifies what he means in the latter half of the quote that while we “declare” the sanctify of God’s name as a fact, it is all together different when God justifies the sinner. His act of justification actually transforms the sinner or “makes those to be saints who were not saints before.”