When the Gospel is not understood as the gracious promise of God alone, the forgiveness of sins for Christ’s sake, not only is the Gospel lost, but faith is recast into something other. When the common, basic understanding of the Gospel as unconditional promise is forfeited by the churches, faith is no longer a, “…response of man to this promise, his trust in the pledge of divine mercy.”  Instead it is made over into, at the same time, a response to God’s command to repent, “which accompanies the promise in the Gospel.”  Thus, writes Hermann Sasse, “faith approaches the idea of obedience.” 
In this way the Westminster Confession of 1647, following Calvin, defined saving faith as, “yielding obedience to the commands [of God], trembling at the threatenings, and embracing the promises of God.” It goes on to say that, “the principal acts of saving faith are accepting, receiving, and resting upon Christ alone for justification, sanctification, and eternal life by virtue of the covenant of grace.” Thus, God does not justify men in fact through the proclamation of the Gospel and the Sacraments. God does not justify men by, “imputing faith itself, the act of believing, or any other evangelical obedience to them, as their righteousness, but by imputing the obedience and sanctification of Christ.”
The Westminster Confession makes this turn away from unconditional promise to conditional response, because they rejected God’s promise of free grace in Christ. They believed there was something besides God’s promise that was also God’s proper work: the Law. If, as Sasse writes, “the proclamation of the divine Law is a part of the ‘real work’ of Christ; if it belongs to the nature of Jesus Christ, as the Savior, to be the Interpreter of the Law and hence also its authoritative Teacher; then obedience to His command is a natural and necessary counterpart of trust in His promise of grace, and saving grace includes both. If, to quote Karl Barth … ‘the Law stands beside the Gospel, on the same footing, as a part of the selfsame eternal treasure,’ then the juxtaposition, ‘on the same footing,’ of obedience to the commandments and trust in the promise cannot possibly be avoided.” 
What we discover in the Calvinist and subsequent Reformed doctrine about faith is, in short, the obedience of the Enthusiasts, which Luther warned the Church about in his Smalcald Articles. The Enthusiasts were not satisfied with the Wittenberger’s teaching about justification, who they accused of using Christ’s graciousness and forgiveness to cover their immoral lifestyle. Instead, they argued, faith must also be tried and proven by obedience to God’s commands, which they were more than eager to supplement with obedience to moral law and the Golden Rule.
However, writes Sasse, “If the Golden Rule constitutes the essential Gospel, and if the keeping of the Rule is Christianity, there is no longer any need for the Lamb of God who bears the sins of the world. In fact, we no longer need Christ even as Lawgiver. For the Golden Rule is also known to the heathen: it is, as old Lutheran theology always insisted, a part of the law written in the hearts of all peoples. And the two-fold commandment to love God and fellowmen is familiar also to the Jews, for it is recorded in the Old Testament.” 
Unfortunately this is the state of modern Christianity. The Gospel is more often than not presented to an atheistic, nihilistic world as a system of morality. Yet, this is not a recent innovation. Listen to the admonition of the Formula of Concord at this critical point, which warns that when we confuse Law and Gospel, obedience and faith: “the Gospel is again converted into the law, the merit of Christ and the Holy Scripture obscured, Christians robbed of true consolation, and the door opened again to the papacy.” [FC, Part I, Chapter V]
This is the temptation which constantly threatens to overwhelm evangelical Christianity in every generation. Therefore, we ought faithfully to listen to what that great cloud of witnesses, especially Hermann Sasse, has to teach us about this dread disease of Law-Gospel confusion which turns Jesus into a new Moses, obscures the importance of Gospel preaching and the Sacraments, and terrifies consciences so they find no certainty in this life; because the unconditional promise of forgiveness is yoked to the, “the obedience of faith, “ as Calvin liked to refer to it. A phrase used very rarely in the New Testament, and which by no means, writes Sasse, “exhausts the Biblical meaning of faith.” 
Note: All citations of Herman Sasse are taken from, “Here We Stand,” pg. 130-132.