Justification and righteousness come by faith alone. I am saved by faith, made righteous by faith and kept by faith in Christ's blood. That is the very foundation of the gospel. But not all faith is justifying faith. The Bible clearly speaks of two kinds of faith: one that justifies and another that is of no value—a faith that even the devils exercise.
The book of Acts records that Simon the magician "believed" but his faith was not the justifying kind. "Simon himself believed also: and . . . he was baptized" (Acts 8:13). Simon offered the apostle Peter money to acquire the power of the Holy Ghost but Peter answered, "I perceive that thou art in the gall of bitterness, and in the bond of iniquity" (verse 23). He was saying, "Your heart is still bound by sin."
Peter told Simon that without repentance both he and his money would perish. Indeed, Simon believed but he was not made the righteousness of God in Christ. His faith was not justifying faith, the kind that purifies the heart and brings the righteousness of Christ.
Scripture says many people "believed [in Jesus] . . . when they saw the miracles which he did. But Jesus did not commit himself unto them... for he knew what was in man" (John 2:23-25). These people had a belief in Christ but it was not the faith of those who receive "power to become the sons of God" (1:12).
Justifying faith is more than a faith of assent; it does more than just acknowledge God. James argued: "Thou believest that there is one God; thou doest well: the devils also believe, and tremble" (James 2.19). James was talking about a dead, temporary faith, not an eternal one. And Jesus warned about this kind of faith, saying that some believe for a while “[but] have no root . . . and in time of temptation fall away" (Luke 8:13).
But there is a justifying faith, one that "purifies the heart" (see Acts 15.9) and "believeth unto righteousness" (Romans 10:10).
In order for faith to be justifying, there must be an accompanying desire to obey and be faithful to God. This kind of faith contains a vital force, a principle of everlasting obedience and love for God.