A Carnal Christian does not mean the person is "as bad as can be" and is engaged in near constant sexual immorality, gambling, or drunkenness. It can come in a nice family-man package. A Carnal Christian can go to church; he can be a deacon, elder, pastor or priest.
The Catholic Church presently has her hands full of Carnal Christian politicians. These are the fairly common pro-abortion, pro-gay-marriage Catholics in and aspiring to office who are appalled that the RCC would dare to point out how their positions are not biblical.
A Carnal Christian might ace a theology exam. But he displays no fruit whatsoever.
This would all be well and good but for one small thing: there is no such animal. Carnal Christians do not exist.
The concept of the myth of the Carnal Christian is surprisingly rich. It touches upon the ancient (and still thriving) heresy of antinomianism. It dovetails into the meaning of free will. And it rears its ugly head in the modern and poorly named "Lordship Salvation" debate.
Not all Christians, by a long shot, would agree that Carnal Christians do not exist. There is, for example, a great deal of attention paid to them in the literature of the Campus Crusade for Christ.
Nevertheless, I think they do not exist. A Carnal Christian is merely carnal. He may be masquerading as a Christian. He may even believe he is a Christian. But in reality he is just your garden variety unbeliever.
A so called Carnal Christian is at best a heretic. The heresy is antinomianism: the belief that if we are free of the law then we can ignore the law.
Free from the lawPaul addresses the heresy full force in Romans, summarized nicely by Romans 6:1-2.
Oh blessed condition
I can sin all I want
And still have remission
The book of James also utterly refutes the very concept of a Carnal Christians. If you are saved, then your faith is not dead. But James writes that a faith without works is a dead faith. Ergo, a Carnal Christian, by definition without good works (except, possibly, for imitations) has a dead faith. So a Carnal Christian is not saved and therefore is not a Christian at all.
It is impossible to be regenerated by the Spirit and not have your life changed. It may not be outwardly radical, and it may be slow, but your life will change. James offers no probationary period where you are excused from works yet your faith is alive.
The Lordship-Salvation controversy is between those who teach that you can accept Christ as Savior but not, at least immediately, as Lord, and those (count me among them) who say that such a view is contrary to scripture. Counter charges of antinomianism and salvation-by-works were (and are) fired back-and-forth.
In short, the Lordship Salvation debate was really between those who affirm the existence of Carnal Christians and those who deny it.
No model of the free will is, in my opinion, completely satisfactory. However, as an explanation of the gross features of free will I follow, as I have written about many times, the basic Augustinian, Lutheran, and Edwardsian (and hence Reformed) notion that free will means not only are we free to choose what we want, but in fact we always choose what we want most. More importantly, we never choose what we don't want. And what we don't want before regeneration is God:
THERE IS NONE WHO UNDERSTANDS, THERE IS NONE WHO SEEKS FOR GOD; (Rom 3:11)According to this view, after regeneration our desires are changed. We are made alive. We are given a heart of flesh (in this case, when contrasted with a heart of "stone", flesh is good, not bad.) We now seek God of our own free will. That same new will shall inevitably seek additional ways to please God. Those additional ways are the very definition of good works, and the very antithesis of carnality.
On the other hand, what of, not a Carnal Christian, but a Christian who is carnal? This is a related topic. But that is where the similarity ends. A Christian who is carnal is one who fights a constant battle between conflicting desires to please God and to seek the pleasures of the world. That would include all Christians. The Apostle Paul spoke crystal clearly on this matter in Rom 7:14-19. Occasionally you meet a Christian who will say that he has received the "second blessing" and is free from sin. Such a person is misguided. He is also arrogant, claiming righteousness far beyond what the Apostle Paul wrote of himself.