According to Acts 11:26, the followers of Jesus were first called Christians at Antioch. Why were they called Christians? Because they were “followers of Christ.” They had committed their lives to “walk as Jesus did” (1 John 2:6).
Other Scriptures explain how a person comes to faith in Jesus Christ and begins this relationship. For example, Ephesians 2:8-9 reveals that a person becomes a Christian by faith, not by following a list of rules or good works: “For by grace you have been saved through faith. And this is not your own doing; it is the gift of God, not a result of works, so that no one may boast.” A true Christian has faith in Jesus as the Savior.
Romans 10:9-10 says, “If you confess with your mouth that Jesus is Lord and believe in your heart that God raised him from the dead, you will be saved. For with the heart one believes and is justified, and with the mouth one confesses and is saved.” A true Christian is unashamed to say Jesus is Lord and believes Jesus was resurrected from the dead.
First Corinthians 15:3 says this message of the resurrected Jesus is of “first importance.” Without Jesus’ resurrection our faith is “futile,” and we are “still in [our] sins” (v. 7). A true Christian lives by faith in the resurrected Jesus (1 Corinthians 15:13-14).
Paul writes, "If anyone does not have the Spirit of Christ, he does not belong to Christ. . . . The Spirit himself testifies with our spirit that we are God’s children" (Romans 8:9, 16). A true Christian has God’s Holy Spirit living within.
The evidence of a true Christian is displayed in both faith and action. “If anyone is in Christ, he is a new creation; the old has gone, the new has come!” (2 Corinthians 5:17). James says, “I will show you my faith by my works” (James 2:18). Jesus put it this way: “I am the light of the world. Whoever follows me will never walk in darkness, but will have the light of life” (John 8:12). A true Christian will show his faith by how he lives.
Despite the wide variety of beliefs that fall under the general “Christian” label today, the Bible defines a true Christian as one who has personally received Jesus Christ as Savior, who trusts in the death and resurrection of Jesus Christ alone for forgiveness of sins, who has the Holy Spirit residing within, and whose life evinces change consistent with faith in Jesus.