Salvation is by God's grace and is received through faith. Faith implies not only intellectual assent, but action. The illustration of a chair is commonly used. To truly have faith in a chair, one must sit in it. A person can "believe" that the chair will support their weight. They may even recognize they have a need to be supported by the chair. But they do not exercise faith until they actually sit in the chair. Similarly, a person can "believe" in some senses of the word without actually being saved.
Is it possible for a person to believe in some way and yet not be saved?
James 2:19 says, "You believe that God is one; you do well. Even the demons believe—and shudder!" Believing that God exists is not saving faith. To be saved, a person must acknowledge that it is the God of the Bible who exists, that we have all sinned and are deserving of punishment (Romans 3:23; 6:23), that we cannot save ourselves (Ephesians 2:8–9), and that the only means of salvation is through Jesus Christ (John 14:6; Acts 4:12). The fact of the existence of God is evident to everyone (Romans 1:20). Acknowledging this fact is not sufficient for salvation.
What about someone who "believes" in Jesus? Admitting that Jesus was a good teacher or even a prophet is not saving faith. We must acknowledge that Jesus is God in human flesh, lived a perfect life, died in our place, and rose again from the dead to conquer death and sin and offer the gift of salvation. In Matthew 7:21–23 Jesus, said, "Not everyone who says to me, 'Lord, Lord,' will enter the kingdom of heaven, but the one who does the will of my Father who is in heaven. On that day many will say to me, 'Lord, Lord, did we not prophesy in your name, and cast out demons in your name, and do many mighty works in your name?' And then will I declare to them, 'I never knew you; depart from me, you workers of lawlessness.'" Some have erroneously used this passage to suggest that salvation can be lost. Jesus is not saying that we must work to maintain salvation or that we can lose salvation. These are people that Jesus never knew. People may pay lip-service to Jesus or even be involved in ministry without actually knowing Him. They appear to acknowledge Jesus and yet have no relationship with Him. They have not been born again.
Jesus also talked about those who may initially respond positively to the gospel, and yet never really be saved. The parable of the sower in Matthew 13 talks about this. We see one example in Judas, who was a disciple of Jesus and yet betrayed Him. Judas appeared to follow Jesus, yet he ultimately did not truly believe Him. In John 6 we learn about people who had followed Jesus and listened to His teachings, but Jesus knew that some of them didn't believe, and many then turned away from Him.
Salvation is by God's grace alone and received through faith. Faith implies some action on our part, it is a reliance on God. Belief unto salvation is a belief that transforms us. It isn't an intellectual agreement only, but a recognition of our hopelessness apart from God and His gracious offer to save us. Then we act on that belief by putting our faith in Jesus. As a result, we are born again, invited into relationship with God, and our lives are changed.
What is faith in Jesus? What does it mean to have faith in Jesus?
How can a believer have assurance of salvation?
Is salvation by faith or works or both?
Is salvation about more than just the afterlife?
How can I be saved?
Truth about Salvation