Charles Hodge has an excellent (long, but excellent) Systematic Theology on Reformed Theology. One reason that it is excellent, is that he takes much of his book to examine the differences between the Reformed tradition and others.
In his excurses on justification, Hodge examines the differences between the Reformed concept of justification to that of the Catholic and Arminian tradition.
First, Hodge describes the Reformed concept of justification as,
a judicial or forensic act, i. e., an act of God as judge proceeding according to law, declaring that the sinner is just, i. e., that the law no longer condemns him, but acquits and pronounces him to be entitled to eternal life.
Hodge clarifies further by saying that justification is not,
simply pardon and restoration. It includes pardon, but it also includes a declaration that the believer is just or righteous in the sight of the law. He has a right to plead a righteousness which completely satisfies its demands.
So for a Reformed understanding of justification, there is both a negative — pardon of sins — and a positive — imputation of justice. This is because Christ, as head of the elect sinner, positions himself in his place. And in his stead, Christ endures the punishment of sin, and obeys the requirements of the law.
And so justification is an extrinsic, declarative act of God. It is an unchanging objective reality in which God “declares that notwithstanding [the sinner’s] person sinfulness (actual) and unworthiness, he is accepted as righteous on the ground of what Christ has done for him”. As Christ is righteous, so God says of the sinner.
In contrast, Hodge brings in the differing doctrines on justification, first the Roman Catholic concept. He describes this concept of justification as
subjective justification. That is, that justification consists in an act or agency of God making the sinner subjectively holy. Romanists confound or unite justification and sanctification. They define justification as “the remission of sin and infusion of new habits of grace.” By remission of sin they mean not simply pardon, but the removal of everything of the nature of sin from the soul. Justification, therefore, with them, is purely subjective , consisting in the destruction of sin and the infusion of holiness.
By this, what he means to say is that justification is not objective, extrinsic, but the opposite. It is the act of God, whereby he makes the sinner subjectively, ontologically, actually holy. That is, justification is pardon of past sins, and the positive infusion (not imputation) of the righteousness of Christ, which makes the sinner just. So what God declares to be just is actually just.
Catholic John Henry Newman says of the Roman concept of justification:
Justification is an announcement or fiat of Almighty God, which breaks upon the gloom of our natural state as the Creative Word upon Chaos; that it declares the soul righteous, and in that declaration, on the one hand, conveys pardon for its past sins, and on the other makes it actually righteous (Lectures on Justification)
By fiat of God, his creative work makes the sinner subjectively just (by participation in Christ). Hodge is right, then, when he says that Roman Catholics “unite justification and sanctification”. Because of this, justification is not objective. It is always changing (for the better or worse). The justified person, by infusion of Christ’s righteousness, can cooperate and grow in justice, or can degenerate and even sin mortally.
After this, Hodge evaluates the Arminian concept of justification. Hodge begins by explaining where Arminius differed from the other Reformers. This difference was of course over the Reformers’ concept of election. But his disagreement of election led him (more particularly his followers) to a different of understanding of justification.
Hodge says of Arminius’ concept of election,
The purpose of election [for Arminius] is not a purpose to save, and to that end to give faith and repentance to a definite number of individuals, but a purpose to save those who repent, believe, and persevere in faith until the end. The work of Christ has, therefore, an equal reference to all men. He made full satisfaction to God for the sins of all and every man, so that God can now consistently offer salvation to all men on the conditions laid down in the Gospel. This is a self -consistent scheme. One part implies, or necessitates the admission of the others.
God’s election and atonement thus change from particular and individual, to universal and open. This, of course, changes one’s view of justification. In the Reformed concept, Christ came to vicariously mediate himself for a particular select group of people by obeying in their place, and dying in their place. In Arminius’ view, Christ came to save anyone who would repent and believe (conditional election).
For this reason, he and his followers — known as the Remonstrants — regarded the atonement as merely satisfaction of justice, and justification as only remission of past sins and acceptance by God.
Hodge is dismissive of this view:
[Arminius’ followers, the Remonstrants,] denied that Christ’s work was a real satisfaction for sin, [and] they of necessity denied any real justification of the sinner. Justification with them is merely pardon.
Obviously, Hodge shows his Reformed colors in saying that the Remonstants denied a “real satisfaction”. What Hodge means to say is that Jesus’ sacrifice was general in nature. It satisfied God’s justice, but not for a specific people, as in the Reformed view. So salvation is open to all, but is not accomplished without the positive response of the individual (which puts the burden on the person, rather than God). More than that, Hodge means to point out that justification for the Remonstrants, is only a pardoning of past sins (negative), and contains no imputation or infusion of Christ’s righteousness (positive). To him, this makes justification lesser than Reformed or Catholic understanding.
As the righteousness of Christ is not imputed to the believer, the ground of his justification, that which is accepted as righteousness , is faith and its fruits, or faith and evangelical obedience.
For the Arminian Remonstrants then, justification is the pardon of past sins, and afterward necessarily requires positive Christian obedience (because there is no imputation).
And so, Hodge covers — I would say fairly well — the three main spectrums of justification. First is the reformed, extrinsic justification, which is not connected subjectively to the believer. Second is the subjective, actual, ontological justification of the sinner in Roman Catholicism. Lastly, is the pardoning justification of Arminius and the Remonstrants.