"Are there carnal Christians- ones who profess to believe and go
immediately back to their old life, who never show evidence
regeneration having taken place?"
Yes, there are “carnal” Christians, but no, there are no Christians who never show evidence of regeneration having taken place. The notion that a person could truly embrace the saving work of Christ while not embracing His Lordship is a pernicious error made most popular by Bill Bright and Campus Crusade for Christ. The “scholarly” support for this distorted perspective has come from Charles Ryrie and Zane Hodges both of whom taught at the dispensational mecca of Dallas Theological Seminary.
This idea has any number of problems. First and foremost is that it divides Christ. It is all well and good to distinguish between the three-fold office of Christ, affirming that He is prophet, priest and king. It is another thing altogether to suggest that one can truly embrace one part of that formula, while passing over another. To embrace the Christ who saves as savior but to reject the Christ who reigns as Lord is to divide Christ.
This notion, secondly, deeply misunderstands how it is that we even come to embrace the saving work of Christ. Because we are, by nature, children of wrath, we are unable, in ourselves, to embrace anything of the work of Christ. Before we can come to Him He must change us first. God the Holy Spirit must change our heart before we can come to faith. This is regeneration, which does not flow from our faith but is the source of our faith. If we have been given a new heart, if our inclination is no longer only toward sin, if we are not only changed by but indwelt by the Spirit, how could we help from growing in grace? He has not only forgiven us, but is cleansing us from all sin (I John 1:9).
Third, this notion cuts off the legs of our assurance. While understanding and affirming the biblical doctrine of God’s saving grace is a critical part of our assurance, it is not enough. The demons, after all, know that Jesus lived a perfect life for us, that He died as a substitute for us, receiving the wrath of the Father due to us for our sins. Our assurance is grounded in our embracing the true gospel, and our changed lives. What sets believers apart from demons and false professors of the true faith is that we are indeed changed. We are not without sin, but we are changed.
Which brings us back to the reality of carnal Christians. The term itself comes from Paul’s admonition to the church at Corinth that the believers there are “carnal.” Do carnal Christians exist? Of course they do. We’re all carnal. That is, we still struggle against our sin nature. We still sin. In that sense all believers are carnal. We are changed by the work of the Spirit, but we are not complete. We are not without sin. Our standard then is not “Am I perfect?” for then no one would qualify as a believer. Instead it is “Am I getting better?” I still struggle against sin. Did I not struggle, were I comfortable with my sin, I would be a carnal “Christian.” That I struggle demonstrates that I am a “carnal” Christian. It is a subtle difference from one perspective. From another it is the difference between eternal life and death.