Faith is a grace of the gospel. And like the gospel it comes to us from outside of us. Saving faith is not something that we conjure up from within, or muster up or build up through self-effort or positive thinking. Rather, saving faith is a gift of God by which we apprehend the good news of Christ crucified "who of God is made unto us wisdom, and righteousness, and sanctification, and redemption" (1 Cor. 29-30). Paul wrote,
For I am not ashamed of the gospel, for it is the power of God for salvation to everyone who believes, to the Jew first and also to the Greek. (Rom. 1:16)
But we preach Christ crucified, unto the Jews a stumbling block, and unto the Greeks foolishness; But unto them which are called, both Jews and Greeks, Christ the power of God, and the wisdom of God. (1 Cor. 1:23-24)
For I decided to know nothing among you except Jesus Christ and him crucified. And I was with you in weakness and in fear and much trembling, and my speech and my message were not in plausible words of wisdom, but in demonstration of the Spirit and of power, so that your faith might not rest in the wisdom of men but in the power of God. (1 Cor. 2:2-5)Faith that is given through the hearing of the gospel is the very same faith that is renewed in the hearing of the gospel. It is faith born of and nourished by the gospel that trusts in Jesus for the forgiveness of sins and the assurance of salvation through him.
Westminster Shorter Catechism Q. 86. What is faith in Jesus Christ? A. Faith in Jesus Christ is a saving grace, whereby we receive and rest upon him alone for salvation, as he is offered to us in the gospel.
That isn't meant to be a one time experience. It's an ongoing means of grace in the Christian life. And it's the gospel of Jesus Christ apprehended through faith that humbles and leads believers into thankful obedience to God. As Westminster Larger Catechism Q/A 97 teaches, the primary function of the moral law for believers is to continue to point them to the gospel causing them to realize how much they...
are bound to Christ for his fulfilling it, and enduring the curse thereof in their stead, and for their good; and thereby to provoke them to more thankfulness, and to express the same in their greater care to conform themselves thereunto as the rule of their obedience.Which echoes Paul's words,
For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast. For we are his workmanship, created in Christ Jesus for good works, which God prepared beforehand, that we should walk in them. (Ephesians 2:8-10)For those who have trusted in Jesus Christ as offered in the gospel, salvation from sin is received by faith as an already judgment before the throne of God. In God's declaration of justification in Christ received through faith, sinners/saints can know that they truly have peace with God (Rom. 5:1; 8:1). And yet in daily experience, the Christian life in many ways is a not yet. We still struggle with sins, many of which easily entangle us. We often struggle to obey. Where is one to find comfort and the assurance of salvation in light of this kind of personal experience? Certainly not from within. Shouldn't we then conclude that in this life we'll always need to hear the good news proclaimed? The word of salvation in Christ is the ongoing means of salvation for the elect and it is still, and always, by grace through faith in Christ alone.
Some additional thoughts...
It is the gospel that God has ordained as the means to bring sinners to Christ. Indeed as Paul wrote in Romans 1:16 "the gospel... is the power of God for salvation unto everyone who believes..." So then where does faith come from? Yes, it is a gift of grace from God himself to the elect. And how does God communicate that gift of grace? Calvin writes:
"God inspires us with faith, but it is by the instrumentality of his gospel, as Paul reminds us, "Faith cometh by hearing" (Romans 10:17). God reserves to himself the power of maintaining it, but it is by the preaching of the gospel, as Paul also declares, that he brings it forth and unfolds it." Institutes 4.1.5Can we then not say that it is upon hearing the gospel that we receive from God the gracious gift of faith by which we believe the very same gospel that we are hearing? And it's that same gospel proclaimed that continues to nourish and strengthen our faith in Christ.
Belgic Confession, Article 24: The Sanctification of Sinners - We believe that this true faith, produced in man by the hearing of God's Word and by the work of the Holy Spirit, regenerates him and makes him a "new man," causing him to live the "new life" and freeing him from the slavery of sin.