Few have said it more clearly. Thanks to Wes for posting this. Please don’t fail to read to the last paragraph:
In discharging this instrumental office faith is entirely alone. It is followed, and in accordance with the provisions of the covenant of grace it is inevitably followed, by the other graces of the Spirit, and by good, that is, holy works; but they do not co-operate with it in the act by which Christ and his righteousness are received in order to justification. They are not concurring causes, but the certain results of justification (emphasis added- rsc).
Girardeau puts the choice squarely before us. Either good works and Spirit-wrought sanctity are the results of justification or a concurring cause. The “covenantal moralists” want them to part of faith co-operating with it in the act of justification. In this way they believe they can secure sanctity from the sinner. Like all rationalists, the do not believe that the Holy Spirit, the power of the Gospel, is a sufficient engine for producing sanctity. They must make justification, in some way, contingent upon our sanctity in order to be sure of our sanctity.