According to the Bible, humanity is clearly responsible to exercise Spirit-wrought faith in Jesus. When sinners willing place their faith in Jesus, God responds by justifying the sinner for their good and his glory. However, before we talk about the necessity of man acting in faith, we should first remember that justification is by grace.
The reality of a gracious or gratuitous and merciful justification means human beings do not earn righteousness by exerting effort. Any attempt to earn God’s favor would undo grace. Interestingly enough, both Rome and the Reformers assert the mercy of God as a leading cause of justification. For Rome, the efficient cause of justification is the mercy or grace of God.  The Reformed have no quarrel in seeing justification as a grace or even admitting that grace is the efficient cause of justification. Calvin writes, “the Scripture everywhere proclaims that the efficient cause of eternal life being procured for us was the mercy of our heavenly Father.” Turretin communicates the same reality. Turretin, in defending a forensic reading of the term justification, says that “Justification is the act…of a supreme magistrate and prince…[who shows] favor to the guilty.” The phrase “showing favor” points to the merciful and gracious character of God’s justifying act. Indeed, “we cling to this foundation.” Question sixty of the Heidelberg Catechism codifies the gracious character of justification.
Q. 60: How art thou righteous before God?
A. Only by a true faith in Jesus Christ; so that, though my conscience accuse me, that I have grossly transgressed all the commandments of God, and kept none of them, and am still inclined to all evil; notwithstanding, God, without any merit of mine, but only of mere grace, grants and imputes to me the perfect satisfaction, righteousness and holiness of Christ.”
In addition, for the Reformed, grace was prior to any human act of the will. Of course, the priority of grace was not a novelty within Christian theology. Augustine believed God’s grace preceded a move of the will towards God. He makes this explicit in reference to justification in his work, The Spirit and the Letter. “Justified, then, not by the law, not by their own will, but the weakness of our will is discovered by the law, so that grace may restore the will and the restored will may fulfill the law, established neither under the law nor in need of law (italics added).” True, this does not mean Augustine had a Reformational understanding of justification sola fide. Yet, he clearly believed in the priority of grace over an act of the will. Indeed, grace must precede an act of the will that moves towards God. In this regard, Aquinas was Augustinian. Aquinas states that “The first [step] is the infusion of grace; the second, the free-will’s movement towards God; the third, the free-will’s movement towards sin; the fourth, the remission of sin.” Thus, as is clear, for an Augustinian, grace is prior to the free-will’s (liberum arbitrium) move towards God.
However, the priority of grace in the thought of Augustine, Aquinas, and, as we shall see, the Reformers stood in contrast to the late Medieval position that we find in men like Gabriel Biel, perhaps the “last of the scholastics.” For Biel, the liberum arbitrium (free will) has “causal priority.” That is, the man who does his best, or does what lies within him (facere quod in set est), would merit de congruo (rather than de condigno)the first grace. The act of the will in doing its best causes grace to flow towards the sinner. Biel writes, “The infusion of grace is granted to the sinner when he does his very best.” Therefore, in summarizing Biel, Heiko Oberman concludes that for Biel, “grace is not the root but the fruit of preparatory good works.” In short, Biel’s form of medievalism had a tremendously elevated view of man. Men and women had the power within them, even post-Fall, to make the first step towards God. If they would first help themselves (facere quod in se est), God would turn and help them with a gift of grace. This is an optimistic anthropology (i.e. elevated view of man) because it assumes fallen humanity has the ability to move towards God apart from an inward work of grace. The idea that the liberum arbitrium is able to move towards God prior to God working graciously within the sinner is firmly rejected by the Protestant Reformers.
The priority of grace over the liberum arbitrium, is clear in the Reformers. Of course, before Calvin and the Reformed tradition assert the priority of grace, it is true that we find Luther debating the Medieval position of those like Biel on this very point. By 1517, in his Disputation against Scholastic Theology, Luther stands firmly “against the via moderna’s anthropological optimism.” That is, contra to Biel, as mediated through Luther’s teacher Johann Nathin, Luther believed grace must precede any move of the will towards God. He writes, “On the part of man, however, nothing precedes grace except indisposition and even rebellion against grace.” Summarizing Luther, Barrett writes, “Grace must be primary, prevenient, and…effectual.” With Luther revolting against the priority of the will over grace, a current found as far back as Augustine and running through those like Aquinas, flowed straight through Luther to the Reformed tradition.
Building on his doctrine of depravity, in which the will has been enslaved to sin, Calvin notes that “When the will is enchained as the slave of sin,” it is impossible for the will “to make a movement toward goodness.” He continues, “every such movement is the first step in that conversion to God, which in Scripture is entirely ascribed to divine grace.” Though Biel asserted that if man would do his best, God would bestow grace, Calvin and the Reformed tradition maintained that man was simply unable to do his best apart from a prior work of grace within the sinner’s soul. To the praise of God, we find that our Lord uses various means (e.g. hearing the Word) to “remove an unbelieving and stony heart [to] create a new heart…[thus] God customarily generates actual faith in the heart.” In short, the Reformed tradition, in continuity with Augustine, Aquinas, and Luther maintains the absolute necessity of a work of grace preceding any move of man’s liberum arbitrium towards God.
In the end, for the Reformed, justification is by grace, which has priority over the will of man. Paul tells the Romans that they “are justified by his grace as a gift, through the redemption that is in Christ Jesus” (Rom 3:24). If you pursue justification by “works of the law,” or through any other human effort, “you have fallen away from grace” (Gal 5:4). Luther wrote that to fall from grace “means to lose the atonement, the forgiveness of sins, the righteousness, liberty, and life which Jesus has merited for us by His death and resurrection. To lose the grace of God means to gain the wrath and judgment of God, death, the bondage of the devil, and everlasting condemnation.” For Calvin, to add any human work to justification was tantamount to a “renouncing of Christ and his grace.” Those are massive implications of falling away from grace! To fall from grace is to fall into destruction. By the grace of God and with the help of the Spirit, we cling to grace because “being justified by his grace we…become heirs according to the hope of eternal life” (Titus 3:7). It seems to me, holding to the priority of the will over the priority of grace is akin to falling from the idea of grace alone.
Thus, the Reformation tradition has maintained the gratuitous and merciful nature of justification. More than that, the tradition has asserted the priority of grace. God must work in us before we can move towards him. Our hope is founded upon the reality that God first moves graciously towards us and works within us before we come to him in faith. We thus are dependent upon God’s grace from the first to the last. As Owen writes, “the whole of our acceptation with him seems to be assigned to grace, mercy, the obedience and blood of Christ; in opposition to our own worth and righteousness, or our works and obedience.” Owen continues, it is wisest for those seeking justification before God “to betake himself absolutely, his whole trust and confidence, to sovereign grace and the mediation of Christ.” Here, then, we should follow the Belgic Confession and lean on the Apostle Paul. “And [Paul] saith, that we are justified freely by his grace, through the redemption which is in Jesus Christ.”
 According to the Tridentine Decree on Justification, the efficient cause of justification is the mercy of God (see McGrath, iustitia Dei, 325). In the Catechism of the Catholic Church (1991), justification is defined as a grace in several places (see Catechism of the Catholic Church, 68, 81, 125).
 Calvin, Justification, 4.17.
 Turretin, 27–28.
 Belgic Confession, Article 23.
 John Burnaby, ed., Augustine: Later Works (Louisville, KY: Westminster John Knox Press, 2006), 205.
 Barrett, “Can This Bird Fly: The Reformation as Reaction to the Via Moderna’s Covenantal, Voluntarist Justification Theology,” in The Doctrine on Which the Church Stands or Falls, 628.
 Michael Horton references Biel in this manner in volume 1 of his two-volume work on justification (Horton, Justification, vol. 1, 150). We should remember, however, that Biel does not appear out of a theological vacuum. Instead, he stands in the nominalist tradition and is preceded by John Duns Scotus (1265–1308) and William of Ockham (1285–1347). As Horton notes, though Luther did not care much for Aquinas, at the Heidelberg Disputation in 1518, he likely reacted against Scotus, Ockham, and Biel more so than Aquinas (see Horton, 131–134).
 Ibid., 642.
 Greg Allison explains the difference between condign merit(i.e. true merit)and congruous merit (i.e. appropriate merit). “Merits are of two types: Condign merits are real merits, or merits of worthiness, accomplished by the faithful through divine grace. God is morally obligated to reward the faithful who are righteous with condign merits. Congruous merits, or merits of fitness, are not strictly merits; rather, they are human works reckoned as merits because in doing them, the faithful do what is in them to do. Considered in and of themselves, good works do not achieve any real merit—condign merit—before God, because the faithful who engage in good works are in a state of sin and have received everything—especially grace—from God in the first place. But as long as the faithful do what is within their ability to accomplish, according to the way that God has designed them to use their free will to do good, they are rewarded with congruous merit” (Gregg R. Allison, Roman Catholic Theology and Practice: An Evangelical Assessment (Wheaton, IL: Crossway, 2014), 240. Also, Bernard J Wuellner, Dictionary of Scholastic Philosophy (Fitzwilliam, NH: Loreto Publications, 2012), 75.
 Barrett, “Can This Bird Fly,”639.
 Heiko A Oberman, The Harvest of Medieval Theology: Gabriel Biel and Late Medieval Nominalism. (Grand Rapids, MI: Baker Academic, 2001), 140.
 Alister McGrath has argued that Biel escapes the charge of Pelagianism and Semi-Pelagianism because of the presence of the pactum. That is, in Biel’s scheme, God has voluntarily covenanted to accept man’s doing his best as meriting de congruo the first grace. Thus, the gracious character of the pactum means, for Biel, grace does in some sense precede the act of man’s liberum arbitrium. In arguing this way, McGrath is rejecting the position of someone like Heiko Oberman who believes Biel sits firmly in the Pelagian or semi-Pelagian camp. Oberman writes, “Sin has not made it impossible for man to act without the aid of grace” (Oberman, Harvest of Medieval Theology, 164). Matthew Barrett outlines the argument and, though he appreciates the nuance of McGrath, he finally sides with Oberman. For my part, it seems the debate over Pelagianism is not so much concerned with God’s gracious decision in eternity to past to save sinners. Instead, the question of Pelagian and semi-Pelagianism aims at what fallen man is able to do as fallen man. Fallen man, corrupted by sin, is simply unable to move his own will towards God without an internal work of grace. For a discussion of this debate, see Barrett, “Can This Bird Fly,” 638–642.
 John Calvin, Institutes of the Christian Religion, trans. John T McNeill (Louisville, KY: Westminster John Knox Press, 2006), 180–181.
 Peter van Mastricht, Theoretical-Practical Theology, ed. Joel R. Beeke, trans. Todd M. Rester, vol. 2 (Grand Rapids, MI: Reformation Heritage Books, 2018), 27, 35.
 The phrase “works of the law” is the center of exegetical and theological debate. See Schreiner, Justification by Faith Alone, 97–111. Also, see Schreiner, “‘Works of Law’ in Paul,” NovT 33 (1991): 217 – 44; and I. H. Marshall, “Salvation, Grace, and Works in the Later Writings in the Pauline Corpus,” NTS 42 (1996): 339 – 58.
 Luther, Galatians, comments on Galatians 5:4 (Accordance version). John Piper places things in sharp relief when he writes, “And if we are severed from Christ, there is no one to bear our curse…” (John Piper, The Future of Justification: A Response to N.T. Wright (Wheaton, IL: Crossway Books, 2007), 15).
 Calvin, Galatians (see my accordance notes).
 Owen, The Doctrine of Justification by Faith, 38.
 Beeke, Three Forms of Unity, 40.