This piece can honestly be viewed separately from the larger series on the sufficiency of the Scriptures as the sole, infallible authority for Christian faith and life. Here, I’ll briefly expound on the historical Baptist distinctive of the New Testament as the sole, infallible authority for church polity.
What in the world is “church polity!”, you ask? It basically means “how you do church.” The way you conduct services, make rules, choose Pastors, discipline current members, accept new members and determine what Christian ordinances are (among other things) is called “polity.” Baptists have historically believed the New Testament is the “manual” for church polity.
The New Testament is the progressive fulfillment of the Old. It introduced an entirely new arrangement for God’s rule over the earth, and corresponding new responsibilities for man. If God has introduced a new arrangement and revelation for mankind, as He has done in the past (Heb 1:1), then it is clear man’s authority for proper worship during this period is that new revelation.
Man’s responsibility in any dispensation is to worship God in the way He commands by (1) an authentic, heartfelt response which takes (2) the appropriate form. The genuine response of the believer has always been an unchanging requirement. Rolland McCune observed; “faith in God’s revelation was required not only for redemption from sin but also for fulfilling one’s dispensational obligations,” (Gen 15:6). The form of that response, however, has changed throughout human history as God periodically alters the method of His rule and gives new revelation. That form of response changed with the ministry of Christ; therefore the Baptist position is that the New Testament is the sole, infallible authority governing church matters.
From this basic principle, every other Baptist distinctive flows. It is precisely because the New Testament alone is the sole authority for church matters that Baptists have traditionally held to the following doctrines:
Regenerated and immersed church membership. The Old Testament knows nothing of regenerated membership, for Israelites were born into the covenant family, but “not all who are descended from Israel belong to Israel,” (Rom 9:6b). Likewise, the concept of believer’s baptism after confession of sin in the manner of John (Mt 3:6) was foreign to OT.
Autonomy of the local church. The church itself was a mystery to the OT, a new entity revealed by Christ (Gal 1:12; Eph 3:1-13). The very concept of an autonomous local assembly (“church”) worshipping Jesus Christ as Messiah is blasphemous in an OT context of corporate worship; hence the persecutions the early Christians suffered at the hands of the Jews as a “sect.”
Priesthood of the believer. Christ is our High Priest, who intercedes for us (Heb 9:24). We have direct access to God the Father through Christ our mediator (1 Tim 2:5) and advocate (1 Jn 2:1). Christ’s role is only foreshadowed in the OT; the office of the Levite priestly function was “symbolic for the present age,” (Heb 9:9).
Soul liberty. As a member of a local, autonomous church body, man is responsible and accountable to God alone for his faith and practice (Rom 14:5, 12). “When a Baptist shall rob one man of soul-liberty, by statute, penalty and sword, he will cease to be a Baptist for that reason.
Immersion and the Lord’s Supper. These two ordinances of the New Testament local church are utterly unknown to the Hebrew Scriptures.
Separation. The concept of being set-apart and separate for the Lord in accordance with divine revelation is not a new one (Lev 18:24-19:2). The New Testament, however, has new revelation and doctrine for this present age which was unknown to the prophets of old. Biblical separation, in this or any dispensation, is grounded on the foundation of the holiness of God (1 Pet 1:15-16).
Baptists have always held the Scriptures to be the sole authority for Christian faith and life. They have implicitly held the New Testament alone to be the source for church polity, although historically this has apparently not been a distinction worth making.
John Smythe, who founded what is generally considered to be the first General Baptist church in history in 1609, wrote merely that,
the Scriptures of the old Testament are commanded to the Church, as also the Scriptures of the new Testament . . . the Holy Scriptures are the fountayne of all truth . . . they are the ground and foundation of our faith . . . by them all doctrynes & every Spiritt is to be judged.
The 1689 London Baptist Confession observes, “the Holy Scripture is the only sufficient, certain, and infallible rule of all saving Knowledge, Faith and Obedience.” The 1833 New Hampshire Baptist Confession speaks of only the “Holy Scriptures” as a whole. The 1834 Confession of Free-Will Baptists speaks of both the Old and New Testaments, and asserts, “they are a sufficient and infallible guide in religious faith and practice.
A number of 19th century Baptists made the explicit claim that the New Testament alone is the source for church government:
The fact that Baptist churches alone consistently adhere to the New Testament as an absolute and complete guide, in matters of practice as well as in matters of doctrine, is freely and heartily admitted by many of the ablest defenders of other systems.
Baptists differ fundamentally from Pedobaptists in practically adhering to the New Testament as the sufficient, the exclusive, and the absolute rule of faith and practice. The soul of Baptist churches is submission and conformity to the New Testament.
The reasons behind this explicit stand are unclear, but a covenantal hermeneutic appeared drive at least one 19th century Baptist to this position. Francis Weyland wrote that he “believes the New Testament to be the standard by which the precepts and teachings of the former revelation are to be judged, and that, thus, it is our only rule of faith and practice.
More recently, Richard Weeks elevated the explicit use of the New Testament alone for church polity to a Baptist distinctive in his own writings. Several fundamental Baptist contemporaries from the latter half of the 20th century did not make this hard and fast distinction and continued to speak generically of “the Scriptures” to govern church polity.
Weeks’ formulation of the New Testament as the explicit, sole rule of faith and practice in church polity was correct and unusually precise, much more so than the numerous creeds and confessions which had come before. It accords perfectly well with Thomas Armitage’s statement:
This fact is perfectly clear, namely: That the New Testament contains all that entered into the faith and practice of the Apostolic Churches. Whether it contains little or much, it covers all that they had, and all that we have, which has any claim on the Churches of Christ. It is the only revealed record of Christian truth. 
 Renald Showers’ definition of a “dispensation” is particularly appropriate here: “A dispensation is a particular way God administers His rule over the world as He progressively works out His purpose for world history.” Renald Showers, There Really is a Difference! (Bellmayr, NJ: Friends of Israel, 1990), 30.
 Rolland McCune, A Systematic Theology of Biblical Christianity, 3 vols. (Detroit: MI, DBTS, 2009), 1:125.
 William B. Johnson, “The Gospel Developed,” in Polity: Biblical Arguments on How to Conduct Church Life, ed. Mark Dever (Washington, D.C.: Center for Church Reform, 2011), 168. Johnson, writing in 1846, clearly laid out the Baptist distinctive in his article:
“The denomination to which I have the honor to belong, holds the true fundamental principles of the gospel of Christ. These are, the sovereignty of God in the provision and application of the plan of salvation, the supreme authority of the scriptures, the right of each individual to judge for himself in his views of truth as taught in the scriptures, the independent, democratical, Christocratic form of church government, the profession of religion by conscious subjects only, and the other principles of scripture truth growing out of these or intimately connected with them.”
 Leon Morris, The Gospel According to Matthew (Grand Rapids, MI: Kregel, 1992), 56. “The Jews employed baptism in admitting Gentiles as proselytes, but the sting in John’s practice was that he applied it to Jews!”
 Thomas Armitage, Baptist Faith and Practice (Roger Williams Heritage Archives, 1890), 37.
 Leon MacBeth, A Sourcebook for Baptist Heritage (Nashville, TN: Broadman, 1990), 13.
 Philip Schaff, The Creeds of Christendom, with a History and Critical Notes, Volume III: The Evangelical Protestant Creeds, with Translations (New York: Harper & Brothers, 1882), 742.
 Albert H. Newman, “Baptist Churches Apostolical,” Baptist Doctrines, ed. C.A. Jenkens (Watertown, WI: Roger Williams Heritage Archives, 1890), 236–237.
 Thomas Pritchard, “The Difference Between a Baptist Church and All Other Churches,” Baptist Doctrines, ed. C.A. Jenkens (Watertown, WI: Roger Williams Heritage Archives, 1890), 309.
 Francis Wayland, Notes on the Principles and Practices of Baptist Churches (Roger Williams Heritage Archives, 1857), 92.
 David Saxon, “Maranatha is Baptist,” Maranatha Baptist Theological Journal MBTJ 01:1 (Spring 2011), 20-21.
 For example, see Monroe Parker, “Baptists and Evangelism,” Central Bible Quarterly CENQ 04:3 (Fall 1961), 43: “in all matters true Baptists point to the Bible as the only rule of faith and practice.” See also Warren Vanhetloo, “Convicted Conservative Baptist Beliefs,” Central Bible Quarterly CENQ 04:1 (Spring 1961), 25: He lists the Baptist distinctives and states Baptists believe “in the Bible as the only rule of faith and practice.”
 Thomas Armitage, A History of the Baptists (Roger Williams Heritage Archives, 1886), 117.