There ought to be a law against defining legalism improperly and abusively. ;-)
In 1719 Scottish Presbyterianism erupted into open conflict over "The Marrow Controversy." At the center of the dispute was a 1645 treatise by Edward Fisher (1627-1655, authorship disputed) entitled The Marrow of Modern Divinity. The most influential members of the Church of Scotland decried Fisher's work as antinomianism (and gave the same treatment to the person and the theology of Thomas Boston, who had reprinted The Marrow of Modern Divinity in 1718). The Marrow of Modern Divinity is not an antinomian work (this is a tough mistake for any impartial reader to make—a refutation of antinomianism occupies roughly half of the book's subject matter). The book is important for its refutation of two nefarious foes to the gospel. It is important for the historical controversy that it occasioned in the 1710s. It is perhaps most persistently influential and important for having introduced to the English language the word "legalism."
Fisher defined legalism exceedingly well, contrasting it with the gospel.
Here is the difference [between legalism and the gospel]; the one saith, "Do this and live"; and the other saith, "Live, and do this"; the one saith, Do this for life; the other saith, Do this from life…
As Fisher so cogently indicated, the differences among the gospel, antinomianism, and legalism lie in the relationship between human doing and eternal life. The legalist believes that eternal life comes at least in part as a result of what a human being does. The antinomian denies that human behavior, or the obligation to meet particular standards of human behavior, is a result of eternal life.
Let me be clear: When you call someone a legalist, you are saying that they are lost. You are denying that such a person is a Christian. If you accuse someone of teaching legalism, you are accusing them of teaching another gospel, and you assign to them Paul's anathema (Galatians 1:8), so you are necessarily saying that they are not believers and that they are destined to Hell.
To accuse someone of being an antinomian or of teaching antinomianism is far less severe, although serious. The New Testament refutes those who make God's grace an occasion for sin (Romans 6:1-2). The New Testament is filled with behavioral prohibitions and commands, perhaps given nowhere else as poignantly as they appear in the list of the works of the flesh and the fruit of the spirit—indeed, the entire chapter of Galatians 5 is an exquisite argument against antinomianism (Galatians 5:1-26). However, the proponent of antinomianism is never placed under anathema in the New Testament, nor is antinomianism condemned as a defect in the gospel. Instead of an anathema, the Bible censures antinomianism with Paul's "May it never be!"
NOTE: The New Testament does question the validity of the faith of anyone who lives in an antinomian fashion ("faith without works," James 2:14-26), but it is important to note that a great many theoretical antinomians have been people who, themselves, lived very pious lives. In other words, it is possible to live a life of holiness while believing that it is not very important to do so.
I have accused people before of teaching antinomianism, and I believe that antinomianism poses a serious risk to twenty-first-century American Christianity. Individual liberty, defiance in the face of authority, and the rejection of absolute truth being as prevalent as they are in our society at large, Christians who exist as a part of our society are uniquely vulnerable to antinomian teaching. Indeed, in our zeitgeist it is so much more acceptable to oppose legalism than it is to accuse someone of lawlessness (antinomianism) that Tullian Tchividjian has nonsensically tried to reclassify antinomianism as a kind of legalism just to be able to decry it with a clear conscience (see here). That error which we are unwilling even to denounce by name and on its own terms is the real danger of our time. Nevertheless, I recognize that I must be very careful in speaking of antinomianism, for to apply that label is to accuse a brother of being in serious disobedience against Christ. So much the more so must we be careful when dealing with matters of heresy like legalism.
Perhaps it would be helpful at this point to delve into specifics in order to carry the overall discussion forward. In years past, many Southern Baptists have regarded the use of playing cards as sinful. Southern Baptists were not alone in this conviction; Wheaton used to prohibit students from owning playing cards. My grandfather-in-law, in order to become a deacon at a Southern Baptist church, had to promise to stop playing Pinochle—he wasn't gambling, but he was using playing cards, and this was regarded as sinful by the church.
I think that the church was wrong. I do not believe that it is inherently sinful to employ playing cards (although I can think of sinful things that one could do with playing cards). I have played Spades, Hearts, Solitaire, and a number of other card games. I have never gambled. I do not believe that I have sinned in my card-playing.
Was this legalism, this prohibition of card-playing employed in so many Southern Baptist churches? No. It was error. It was wrongful. It was not legalism, however, unless some church somewhere was teaching that abstaining from card-playing produced, at least in part, eternal life, or that card-playing could undo or block eternal life (and I know of no church that taught any such thing). Whatever these churches' ecclesiology or doctrine of the Christian life, they were not engaging in legalism unless their soteriology had become fatally implicated.
Someone will object that Paul made grace the cause of sanctification as well as the cause of justification (Galatians 3:1-3). Certainly this is true, but in the card-playing example above (and in so many of the more puerile discussions about legalism that take place), the topic in view is not the cause of sanctification, but rather the content of sanctification. both old-timey non-card-playing Southern Baptists and new-fangled card-playing Southern Baptists agree that sanctification is caused by grace; one group believes that grace will bring you to abandon card-playing while the other believes that grace will leave your card-playing ways alone. Only one of these points of view can be correct, but neither one is an example of legalism.
This is an important point. We can charge the folks who required my grandfather-in-law to put away his Pinochle cards with something, but at the most it will be something as serious as antinomianism rather than a gospel heresy like legalism. We cannot call them legalists. We cannot call them Pharisees. The Pharisees really were legalists. They were lost. To call someone a Pharisee is to say that someone is not a Christian.
What can we say of the person who would accuse Wheaton of legalism during its card-banning years? Such a person is either theologically ignorant or he is deliberately elevating the charges as a rhetorical device. I'm familiar with rhetorical devices, but damnable heresy is too serious a charge to bandy about in order to enhance rhetoric.
Fisher's The Marrow of Modern Divinity took the form of a dialogue among Neophytus (a new Christian), Nomista (a legalist), Antinomista (an antinomian), and finally Evangelista (Neophytus's pastor), the protagonist who sets them all straight. Evangelista was a Calvinist, and I am not, but I nonetheless aspire to be like him, an Evangelista of my own, avoiding the dangers of both legalism and antinomianism.
So, here is the gospel of Jesus Christ: Your attempt to earn self-justification has already failed miserably. You haven't lived up to your own standard of right and wrong, so much the less God's standard. You've well-earned a spot in Hell. Jesus Christ, not content to leave you in that state, died to provide to you eternal life. All who are saved are saved not because of their behavior but in spite of it—from it. Having been rescued from himself and from the clutches of Satan, a Christian is free from the death-sentence of sin and is released from his slavery to sin. He is the recipient of the most extravagant gift of all human history, and as the unworthy recipient of such an astounding gift, he owes to Christ and His amazing love everything: his soul, his life, and his all. By the power of the grace of God he is made able to live according to a standard that was far beyond his reach before, and because his changed heart loves God and sees the great obligation to Christ that is now his, he wants to live according to that new standard of behavior.
We can believe together all of the preceding paragraph and yet be wrong in different ways about the content of God's standard for our behavior. As we dialogue about those differences, may we do so with accuracy and charity, as well as with resolve and conviction.