This is a great quote from a Protestant expert on the subject of justification. Alister McGrath (Wycliffe Hall, Oxford) literally wrote the book on the subject. Here he describes St. Augustine’s understanding of justification:

Man’s righteousness, effected in justification, is regarded by Augustin as inherent rather than imputed, to use the vocabulary of the sixteenth century. A concept of ‘imputed righteousness’, in the later Protestant sense of the term, would be quite redundant within Augustin’s doctrine of justification, in that man is made righteous in justification. The righteousness which man thus receives, although originating from God, is nevertheless located within man, and can be said to be his, part of his being and intrinsic to his person. An element which underlies this understanding of the nature of justifying righteousness is the Greek concept of deification, which makes it appearance in the later Augustinian soteriology.

Alister McGrath, Iustitia Dei – A History of the Christian Doctrin of Justification, Second Edition, pp. 31-32.