What’s the background of the doctrine of justification by faith? That is, what presuppositions do we hold that make the doctrine of justification necessary and important?
Well, the discussion concerning justification is built on fundamental presuppositions. Namely, that men and women are in need of God’s justification because of their sin. That is, men and women are born sinners and are therefore under God’s wrath (cf. Rom 5:10). The Reformed tradition has consistently noted the need for sinners to understand their plight if they would rightly understand the doctrine of justification. Specifically, sinners must understand their own depravity and at the same time have a sense of God’s majesty if they would grasp justification sola fide.
John Calvin believed that in order to understand justification, we must “apprehend in what situation we stand with respect to God, and what his judgment is concerning us.” For Calvin, due to the sin of Adam, mankind has fallen from grace and stands condemned in the sight of God. Indeed, we “must face the truth of our own miserable condition,” namely that “no sinner can find favor in [God’s] sight, as a sinner, or so long as he is considered as such.” We are all criminals who must stand “before the celestial Judge.” For Calvin, “We must always return to this axiom—That the Divine wrath remains on all men, as long as they continue to be sinners.” In short, Calvin knows justification is the “principle hinge on which religion turns” because it deals with ultimate matters, namely how sinners, those who are at enmity with God (cf. Rom 5:10), can be counted right with their Maker.
John Owen begins his treatise on justification in the same way. Owen writes, “A clear apprehension and due sense of the greatness of our apostasy from God, of the depravation of our natures thereby, of the power and guilt of sin, of the holiness and severity of the law, are necessary unto a right apprehension of the doctrine of justification.” For Owen, however, it was not merely a sense of our own sin that we needed if we would grasp the doctrine of justification. We also need a sense of the majesty of God, “the judge before whom [sinners are] to appear.” Putting both our condition and a sense of God’s majesty together, Owen concludes:
Wherefore, the greatness, the majesty, the holiness and sovereign authority of God, are always to be present with us, in a due sense of them, when we inquire how we may be justified before him…Wherefore, I cannot but judge it best, (others may think of it as they please), for those who would teach or learn the doctrine of justification in a due manner, to place their consciences in the presence of God, and their persons before his tribunal, and then, upon a due consideration of his greatness, power, majesty, righteousness, holiness, of the terror of his glory, and sovereign authority, to inquire what the Scripture, and a sense of their own condition, direct them to, as their relief and refuge, and what plea it becomes them to make for themselves.
The sentiment expressed by Calvin and Owen is not unique within the tradition. Turretin writes, “Here then is the trust state of the controversy. When the mind is thoroughly terrified with the consciousness of sin and a sense of God’s wrath, what is that thing on account of which he may be acquitted before God and be reckoned a righteous person?” For Turretin and the Reformed, the answer was the righteousness of Christ imputed to the sinner. Furthermore, though not always tied explicitly to the doctrine of justification, Reformed confessions have consistently included doctrinal statements concerning the fall of mankind into sin in order to lay the necessary theological foundation prior to statements about justification.
In short, the Reformed tradition begins with the presupposition that mankind stands guilty before God. With David, we confess that we are born in sin (Ps 51:5), having fallen short of God’s glory (Rom 3:23), with death as our wage (Rom 6:23). This is the condition we must rightly grasp if we would come to a right understanding of the doctrine of justification. Second, sinners must recognize the Judge with whom they must deal is majestic, holy, righteous, and just. Before this awesome God, all must appear.
The question of justification, cast in this light, is how can any who have fallen short of God’s glory and rebelled against this holy God hope to stand on the final day? Rome answered the question one way, the Reformed tradition another. For the Reformed, the only hope for sinners was to come to Jesus in faith. Clinging to Jesus by faith, sinners are forgiven and the righteousness of Christ is charged to their account. Only then, with sins forgiven and clothed in the alien righteousness of Jesus, could sinners stand in the presence of the majestic God.
 These quotes are taken from Calvin’s treatise on justification (John Calvin, Justification by Faith, ed. Nate Pickowicz, trans. John Allen, Kindle. (Peterborough, Ontario: H&E Publishing, 2019)).
 These quotes are taken from John Owen, The Doctrine of Justification by Faith: Through the Imputation of the Righteousness of Christ, Explained, Confirmed, and Vindicated (Grand Rapids, MI: Reformation Heritage Books, 2006).
 Francis Turretin, Justification, ed. George Musgrave Giger and James T. Dennison (Phillipsburg, NJ: P&R Publications, 2004), 14–15.
 For example, though Calvin does not include an article on justification in the Confession of Faith, In the Name of the Reformed Churches of France, before he discusses salvation, he takes time to discuss the effects of Adam’s fall (article 7) and original sin (article 8) before turning to the source of our salvation (article 9). Stating the problem (sin) before considering the solution (God’s gracious salvation) helps the reader grasp the issue in the clearest manner (Calvin, Tracts and Letters, vol. 2., 141–142). The Westminster Confession o Faith (WCF) asserts the fall of man in Article VI before making a statement about justification in article XI.