A mother who was a member of our church came to me one day with a heavy concern. A son of hers who once identified as a Christian had now turned his back on the Christian faith and declared himself to be an atheist. Of course, we all know where the concern lies- did this woman's son lose his salvation by turning his back on Christ?
Before coming to a conclusion on the revocability of salvation in Christ, it's crucial that we first get a deep understanding of a few terms. words including "Christian," "believe," and "faith" are often weakly thrown around in Christian circles so much that we have most likely lost touch of the true essence.
What is a Christian? A Christian is someone who puts his or her full faith and devotion on Christ and believes that what He did on the cross was enough to save us of sin and redeem us from eternal separation from God.
Note however that someone who goes to church, says a prayer, walks down an aisle or joins a ministry is not necessarily a Christian. Remember that Jesus once said that "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." (Matthew 7:21)
Becoming a Christian has more to do with a spiritual and internal realization of who Christ is and what He has done for us. It goes more than just an external behavior and a spoken confession although those things are important.
The Bible tells us that when a believer has a true encounter with Christ and the Holy Spirit, we are marked with an irrevocable seal. Ephesians 1:13-14 says, "In him you also, when you heard the word of truth, the gospel of your salvation, and believed in him, were sealed with the promised Holy Spirit, who is the guarantee of our inheritance until we acquire possession of it, to the praise of his glory."
Can a person who claims to be a Christian leave the faith? Absolutely. But Christianity is not just about claiming to be a part of a religion. Christianity is about being cut to the heart just as the early believers were (Acts 2:37) and getting a true revelation of the Person of Christ, not just the idea of God.
It's hard to turn your back and deny the existence of a person you have met, but easy to do so when you haven't met the person personally. It's the same way with God. A true personal and genuine encounter will be hard to deny and walk away from.