Athanasius (293-373 A.D.) is one of the most influential theologians in Church History. He has contributed much to the Church, but his most famous work is The Incarnation of the Word of God. The purpose of this book is to answer the question, why did the Eternal Son of God become flesh? Athanasius’ answer to this question involves justification.
In The Incarnation of the Word of God, Athanasius places justification within the context of a creation, fall, and redemption. He argues that it is essential that God’s creation was ex-nihilo because it must be dependant upon God for its very existence. When mankind, who is created in the image of God, turns away from God he in fact turns to a corruptibility, which causes a movement towards non-existence: Their natural end is death and destruction. He writes,
For the transgression of the commandment was making them turn back again according to their nature ; and as they had at the beginning come into being out of non-existence, so were they now on the way to returning, through corruption, to non-existence again. The presence and love of the Word had called them into being; inevitably, therefore, when they lost the knowledge of God, they lost existence with it; for it is God alone Who exists, evil is non-being, the negation and antithesis of good.
To him the primary problem of sin is corruption. To support his theology, he largely cites Paul with verses such as 1 Corinthians 15.53, “This corruptible must put on incorruption and this mortal must put on immortality.” Sin produced death and corruption through the law that Adam was given. Mere repentance is not enough to stave off the effects of sin because the problem is the actual nature of man. The problem for Athanasius is primarily ontological in nature, not forensic.
Athanasius’ solution to this ontological corruption is in Jesus’ Incarnation. Jesus, the Eternal Son of God, took on flesh and fulfilled the law by suffering total corruption on the cross on behalf of all who believe in him. For him, it is not so much about a legal verdict but about legal debts being paid off. Adam (and his seed) contractually owes God death for his sin; Jesus paid off his debt by becoming sin and dying on the cross for humanity. Jesus conquered death through his resurrection; therefore, humanity can be renewed in its very being. 
His understanding of imputation is that of corperate association. He likens it to a whole city being honored because of the presence a great king. If we live in his city then we share his glory. How does one enter into His glorious city? We are received into the city through faith.
A good summary of Athanasius’ view on justification is that Christ, the Eternal Son of God, died as a pure and spotless lamb to settle humanities debt by fulfilling the curse of Adam. Through His resurrection, humanity can receive a new nature in which they can live in the world as true humanity was always meant to. Though his view contains forensic elements to it (i.e. legal debt), justification is primarily about the ontological renewal of the image of God.
 Athanasius, The Incarnation of the Word of God, 1.4.
 This can be seen in 2.9 when he states, “For this reason, therefore, He assumed a body capable of death, in order that it, through belonging to the Word Who is above all, might become in dying a sufficient exchange for all, and, itself remaining incorruptible through His indwelling, might thereafter put an end to corruption for all others as well, by the grace of the resurrection. It was by surrendering to death the body which He had taken, as an offering and sacrifice free from every stain, that He forthwith abolished death for His human brethren by the offering of the equivalent.”
 Ibid. 2.9.