“For as the body without the spirit is dead, so faith without works is dead also.” (James 2:26)
James 2:12-26 is concerned to distinguish authentic faith from the mere profession of faith. James critiques the person who “says he has faith” in v.14 and then says in v.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. Our good works do not justify us, but if we do not have them, we do not have the faith through which we lay hold of the justifying righteousness of Christ.
– TableTalk Magazine, June 2017