Because faith is the only instrumental means by which we receive the righteousness of Christ and so are declared righteous heirs of eternal life (Rom. 3:21–4:25), it is critical that we understand what saving or justifying faith is. After all, our Lord Himself warns that on the last day, some will believe that they have been servants of Christ but in fact will be cast out of the kingdom because they never actually believed in Him and hence never did His will (Matt. 7:21–23). We do not want to be numbered among that self-deceived group, and knowing what saving or justifying faith looks like will help keep us from making a false profession of trust in the Savior.
When the Protestant Reformers considered the question of saving faith, they found in Scripture three aspects that are essential for true faith. The first of these is notitia, which is the intellectual content of what we believe. Saving faith is faith in the person and work of Christ, so we must know something about Jesus and what He has done if we are to have actual faith in Him. This is evident from the very existence of the Christian gospel—we tell people about Jesus, giving them biblical content for them to believe.
The second component of saving faith is assensus, or belief that the content of the Christian gospel is true. It is possible to know something and not believe it is true, and in fact we know many things that we do not believe are true, such as the content of other religions. But as the Christian faith is dependent on the historical reality of things such as the resurrection of Jesus (1 Cor. 15:17), we must not only know that Christianity proclaims the content of Christ’s historical resurrection, but we must also believe that the resurrection happened (Rom. 10:9).
Finally, saving faith includes fiducia, which is placing trust in the One revealed in the content that is believed to be true. Knowing what God has revealed and believing it to be true is a good thing, as we read in today’s passage, but it is not enough (James 2:14–19). Even demons know and assent to the truth of God’s revelation, so merely knowing and believing necessary truths for salvation such as the oneness of God are insufficient for redemption (v. 19b). Mere knowledge and belief, as John Calvin comments, “can no more connect man with God, than the sight of the sun carry him up to heaven.” We also need to place our trust in Christ personally to save us. We must believe that Jesus came to save us personally. We must place our lives in His hands, pledging ourselves to follow Him no matter the cost.