James appears to have been a pious Jewish believer. Paul’s letter to the Galatians condemns legalistic men claiming affiliation with James who were teaching the churches in Galatia that gentile believers had to keep the Jewish law in addition to putting their faith in Jesus. Galatians 2:12-13
We don’t have the same wealth of information about the life of James that we have for Paul, but we have enough information to conclude that James became a convert to Christianity because he believed the risen Jesus appeared to him: (1) Early creed (within 5 years of the crucifixion)reports Jesus' resurrection appearance to James (1 Cor. 15;7) and (2) Paul and Acts identify James as a leader in the Church (Gal. 1:19; Acts 15:12-21).
James was executed as a law breaker. He had a reputation for keeping the Jewish law, so it would seem likely that the Law had to relate to his Christological allegiances and a charge of blasphemy. This would fit the fact that he was stoned, which was the penalty for such a crime, and parallels how Stephen was martyred.
The personal appearance of Jesus to his skeptical brother James is part of the church’s earliest tradition, as reported by Paul in 1 Corinthians.
With James, we have a case of a skeptic converting to Christianity based on what he perceived was a personal appearance by the risen Jesus. As with Paul, we must ask the question: What happened to cause James to have such a conviction and hold fast to it unto death?
This is very true....in fact all of the brothers of Jesus were highly skeptical of him and his ministry. One of my favorite examples is how his own brothers tried to get him killed by suggesting he go to the feast in Judea where they knew the Jews were waiting to kill him. Why?....because they did not believe in him. [John 7:1-5]
Evidently his brothers were converted after the resurrection as they were not present at the crucifixion. Earlier they had accused him of being insane. [Mark 3:21] Indeed, Jesus had even publicly insulted his family because of their mistreatment of him. [Matthew 12:46-50]