Some teachers falsely apply the "already/not-yet" scheme to the doctrine of justification, teaching that the "already" aspect of justification occurs at conversion, and is by faith alone on the ground of Christ's active and passive obedience, but that the "not-yet" aspect of justification must be "in accordance with our works."
They cite Romans 2:13 in support: "For it is not the hearers of the Law who are just before God, but the doers of the Law will be justified." In other words, while the believer's justification starts out "by faith alone" (the "already"), by the time the believer stands before the Great Tribunal on the Day of Judgment, his justification is no longer sola fide but according to his works as well (the "not-yet"). Here is a quote from a proponent of this view:
The decision, the judgment, as to who enters the city and who stays outside (for eternity) will be made, on that Great Day of Judgment, in accordance with what you have done in this life...
Who are these people who thus benefit; who stand on the Day of Judgment? They are those who obey the Law who will be declared righteous...
It is justification -- a forensic act of God whereby he declares a person righteous. God is able to make this declaration on That Day because it is a truth. Something has happened to change those who were once sinful. What is it? Our confession [the Westminster Confession of Faith], which so many of my readers profess, says that we who are in Christ Jesus, are sanctified really and personally by the Spirit and Word of Christ to the practice, in this life, of true holiness without which no man shall see the Lord.
According to this view, the Spirit's work of sanctification in us causes us to obey the Law. And it is in accordance with the believer's Spirit-wrought obedience to the Law that God will declare the believer to be righteous on the Day of Judgment and thus qualified to enter the eternal city.
What is the value of the doctrine of justification by faith alone if it is reduced only to the initial justification at conversion? Was the blood of so many Reformers shed in defense of a doctrine that we are only initially justified by faith alone, but that in the end it is really by our own works that we will stand before the Holy Judge of all the earth?
When the Bible says that the believer is justified, it is a statement that the future verdict of righteousness on the last day has already been pronounced in the present. Jesus said, "Truly, truly, I say to you, he who hears My word, and believes Him who sent Me, has eternal life, and does not come into judgment, but has passed out of death into life" (John 5:24).
The true application of the "already/not-yet" to justification is that by faith we "already" experience the assurance of knowing that our "not-yet" justification at the last day has been secured for us by Christ.
Paul said that on the day of judgment he wants to be "found in [Christ], not having a righteousness of my own, derived from the Law, but that which is through faith in Christ, the righteousness that comes from God on the basis of faith" (Phil. 3:9).
This teaching of Scripture is accurately summarized in the Westminster Confession when it teaches that God justifies believers "not for anything wrought in them, or done by them, but for Christ's sake alone … by imputing the obedience and satisfaction of Christ unto them" (WCF XI:1).
The proponents of this view sound orthodox by arguing that the good works of the believer are simply taken into account in a non-meritorious manner at the Day of Judgment. It argues that since sanctification and good works are the result of the Spirit's sovereign work within us, no one can boast before God or take credit for being declared righteous in accordance with one's works. But this fails to recognize that the believer's good works are "mixed with so much weakness and imperfection, that they cannot endure the severity of God's judgment" (WCF XVI:5).
Even if a person could progress in sanctification to such a degree that he attained perfection at the end of his life (this can't be done, but for the sake of argument, if it could) even then, that would not be sufficient. For the Law requires perfect obedience throughout the course of one's life from beginning to end.
This is how Paul interprets the Law when he quotes Deuteronomy 27:26: "Cursed is everyone who does not abide in all the things written in the book of the Law, to perform them" (Gal. 3:10). And again, "Moses writes that the man who practices the righteousness which is based on the Law shall live by that righteousness" (Rom. 10:5).
The Law sets forth two options:
Either you keep the Law perfectly and gain eternal life by it,
or you are under God's curse.
In other words, the Law is a covenant of works. To teach that there is an imperfect, non-meritorious obedience to the Law that will suffice to receive the declaration of righteousness at the Day of Judgment presupposes that the Law's requirements have somehow been lowered or softened.
Following the teaching of Paul and the Reformed tradition, the Law revealed on Mount Sinai was in some sense a covenant of works, and that the Law-Gospel contrast is essential to safeguarding the doctrine of justification by faith alone.
That the Law is nothing more than an administration of the covenant of grace is a novel teaching in the Reformed tradition. If the Law is an administration of the covenant of grace, it follows that New Testament believers are obligated to keep the Law -- not meritoriously or perfectly, but as part of the Spirit's work of progressive sanctification.
But once this groundwork has been laid, and someone comes along and teaches that sanctification is the necessary condition of acquittal at the day of judgment, it is but a small step from sanctification by the Law as a covenant of grace to justification by the Law as a covenant of grace.
This is grace that has been redefined as law. And as Paul said, such "grace" is no grace at all: "If it is by grace, it is no longer by works, otherwise grace is no longer grace" (Rom. 11:6).
Just as Paul warned the Galatian Christians, when the Law's character as a covenant of works is softened so as to allow it to serve in a seemingly harmless role as a means of sanctification, inevitably the Law will become a means of justification.
That is why Paul spends so much time arguing – contra the Judaizers who viewed the Law in gracious terms as something that could be added to faith in Christ – that the Law is not to be trifled with, that those who want to be under it are in danger of placing themselves under a curse (Gal. 3:10), that the Law is not compatible with faith (Gal. 3:12), and that those who try to be justified by it have fallen from grace.
Aesop's fable of the dog who saw his own reflection in the water comes to mind. As soon as he made a grab for the second bone he saw in his reflection, he lost the one in his own mouth. Instead of having two bones, he was left with none. So here - if you try to add the Law to Christ, neither Christ nor the Law will be of any benefit to you (Gal. 5:2-4).