One word—alone—separates the biblical doctrine of justification by faith from the doctrine of justification by faith as defined by Roman Catholicism and several other theological traditions. It is not enough to say that we are justified by faith, for everyone who professes a belief in sacred Scripture confesses that we are justified by faith. The division is between those who believe, with the prophets and Apostles, that justification is by faith alone (Gen. 15:1–6; Rom. 3:21–4:25; Gal. 3:10–14) and those who believe that justification results from a combination of our faith and our good works.
However, to deny that our good works are in any sense part of the basis of God’s declaration that we are righteous in His sight is not to deny that Christians should—indeed must—do good works. Our good works are related to our justification, but we must understand how they are properly related to God’s justifying verdict. Simply put, good works follow God’s decree of righteousness as the fruit of saving faith.
James 2:12–26 is one of the clearest passages in Scripture on this subject. In this chapter, the Apostle is concerned to distinguish authentic faith from the mere profession of faith. James critiques the person who “says he has faith” in verse 14 and then says in verse 18 that you cannot demonstrate faith without good works. Why are good works the necessary proof that faith is real? The answer is because everyone who has actually trusted in Christ is a new creation (2 Cor. 5:17). God does not declare us righteous based on His transformation of us but only on the basis of the perfect righteousness of Christ (v. 21; see Rom. 5:12–21). Nevertheless, all who have trusted in Jesus alone for salvation have also been transformed by Him and are being renewed from glory to glory (2 Cor. 3:18). They cannot help but do what is right, though imperfectly to be sure. And if there are no good works in the life of a professing believer, that person has not been changed and so has not been given the gift of faith, which requires the change God the Holy Spirit works in our regeneration (John 3:5; Eph. 2:8–9).
In Scripture, the word translated as “justify” sometimes means “prove” or “demonstrate” (Matt. 11:19). That is how James uses it in today’s passage. Our works, James teaches, demonstrate our faith. That is, our faith is justified or proven by our works. As John Calvin comments, we are not justified “by a bare and empty knowledge of God,” but true, justifying faith is outwardly revealed in our desire and efforts to obey the Lord.