It is necessary that Christ should come to our aid; who, being alone just, can render us just by transferring to us his own righteousness. You now see how the righteousness of faith is the righteousness of Christ. When therefore we are justified, the efficient cause is the mercy of God, the meritorious is Christ, the instrumental is the word in connection with faith. Hence faith is said to justify, because it is the instrument by which we receive Christ, in whom righteousness is conveyed to us. Having been made partakers of Christ, we ourselves are not only just, but our works also are counted just before God, and for this reason, because whatever imperfections there may be in them, are obliterated by the blood of Christ; the promises, which are conditional, are also by the same grace fulfilled to us; for God rewards our works as perfect, inasmuch as their defects are covered by free pardon.
Commentary on the Epistle of Paul the Apostle to the Romans (Bellingham, WA: Logos Bible Software, 2010), 138–139.