On Romans 1:17
“If we seek salvation, that is, life with God, righteousness must be first sought, by which being reconciled to him, we may, through him being propitious to us, obtain that life which consists only in his favour; for, in order to be loved by God, we must first become righteous, since he regards unrighteousness with hatred. He therefore intimates, that we cannot obtain salvation otherwise than from the gospel, since nowhere else does God reveal to us his righteousness, which alone delivers us from perdition. Now this righteousness, which is the groundwork of our salvation, is revealed in the gospel: hence the gospel is said to be the power of God unto salvation. Thus he reasons from the cause to the effect.
Notice further, how extraordinary and valuable a treasure does God bestow on us through the gospel, even the communication of his own righteousness. I take the righteousness of God to mean, that which is approved before his tribunal; as that, on the contrary, is usually called the righteousness of men, which is by men counted and supposed to be righteousness, though it be only vapor. Paul, however, I doubt not, alludes to the many prophecies in which the Spirit makes known everywhere the righteousness of God in the future kingdom of Christ. Some explain it as the righteousness which is freely given us by God: and I indeed confess that the words will bear this sense; for God justifies us by the gospel, and thus saves us: yet the former view seems to me more suitable, though it is not what I make much of. Of greater moment is what some think, that this righteousness does not only consist in the free remission of sins, but also, in part, includes the grace of regeneration. But I conside, that we are restored to life because God freely reconciles us to himself, as we shall hereafter show in its proper place…As our faith makes progress [this is Calvin’s understanding of ‘from faith to faith’], and as it advances in knowledge, so the righteousness of God increases in us at the same time, and the possession of it is in a manner confirmed. When at first we taste the gospel, we indeed see God’s smiling countenance turned towards us, but at a distance: the more the knowledge of true religion grows in us, by coming as it were nearer, we beheld God’s favor more clearly and more familiarly.
On Romans 3:21-26
It is not certain for what distinct reason he calls that the righteousness of God, which we obtain by faith; whether it be, because it can alone stand before God, or because the Lord in his mercy confers it on us. As both interpretations are suitable, we contend for neither. This righteousness then, which God communicates to man, and accepts alone, and owns as righteousness, has been revealed, he says, without the law, that is, without the aid of the law; and the law is to be understood as meaning works; for it is not proper to refer this to its teaching, which he immediately adduces as bearing witness to the gratuitous righteousness of faith. Some confine it to ceremonies; but this view I shall presently show to be unsound and frigid. We ought then to know, that the merits of works are excluded. We also see that he blends not works with the mercy of God; but having taken away and wholly removed all confidence in works, he sets up mercy alone…
Then the righteousness of God shines in us, whenever he justifies us by faith in Christ.”
—John Calvin, Commentary on the Epistle of St. Paul to the Romans