Theology from A Bunch of Dead Guys™

The Anabaptists
Continue in the faith grounded and settled,
and be not moved away from the hope of the gospel,
which ye have heard" (Colossians 1:23).

he word Anabaptist means "re-baptizer." It is a label often assigned to all "Radical Reformers"—a diverse group that remained outside the mainstream of the Reformation—they were the lunatic fringe of the Reformation. The Radicals ranged from sincere pietists to heretical extremists. One of the latter, Michael Servetus (the anti-Trinitarian who was executed by fire in Calvin's Geneva), was part of the Radical Reformation and is often called an Anabaptist.
But, strictly speaking, the label Anabaptist as it is employed today more properly applies to the less-radical Radicals—men such as Conrad Grebel and Menno Simons, whose movements endure today in Amish and Mennonite communities.
Many Anabaptist ideas made invaluable contributions to the Reformation. For example, these five tenets might be identified as Anabaptist distinctives:

• Sola Scriptura—Anabaptists were sometimes more consistent than the Magisterial Reformers in their insistence on biblical authority for certain practices in matters of church polity and worship.
• Separation of Church and State—Anabaptists correctly saw the church as the assembly of the redeemed, antithetical to the world and sometimes antagonistic to society as a whole. For this reason they advocated separation of church and state.
• Freedom of Conscience—because of the Anabaptists' convictions about the role of the secular state, they believed that the ultimate remedy for heresy was excommunication. They steadfastly opposed the persecution that was so characteristic of their age. They denied that the state had a right to punish or execute anyone for religious beliefs or teachings. This was a revolutionary notion in the Reformation era.
• Believers' Baptism—The anabaptists were the among the first to point out the lack of explicit biblical support for infant baptism. Most of them made no issue of the mode of baptism, and practiced affusion (sprinkling), however, so they were not true baptists in the modern sense of the word.
• Holiness of Life—Anabaptists gave much emphasis to spiritual experience, practical righteousness, and obedience to divine standards. They had no tolerance for those who claimed to be justified by faith while living unfaithful lives. Anabaptists pointed out that Scripture says, "Faith without works is dead" (Jas. 2:20).

On most of those points we would strongly agree with the Anabaptists' thrust (though not necessarily with the extreme conclusions they sometimes came to).
Nevertheless, there is very good reason to approach the Anabaptist movement with a healthy dose of caution. While acknowledging our very real debt to the Anabaptists on the matters enumerated above, we must also recognize an unhealthy tendency in Anabaptist doctrine: Anabaptists rejected the Reformed understanding of justification by faith alone. They denied the forensic nature of justification and insisted that the only ground on which sinners can be acceptable to God is a "real" righteousness wrought within the justified person.
"Menno [Simons], and Anabaptists generally, did not accept Luther's forensic doctrine of justification by faith alone because they saw it as an impediment to the true doctrine of a 'lively' faith which issues in holy living." [Timothy George, Theology of the Reformers (Nashville: Broadman, 1988), 269].
Perhaps it is fair to note that the Anabaptists thought they detected a tendency toward antinomianism in the Reformed doctrine of justification by faith alone. That was what they argued against. But in doing so they undermined the very foundation of the biblical doctrine of justification. They left people to try to devise a righteousness of their own derived from the law, rather than trusting the perfect righteousness of Christ which God imputes to those who believe (cf. Phil. 3:9; Rom. 4:5-6).