To be Reformed Baptist is to affirm the 1689 London Baptist Confession.
If you leave out parts of it, or even go so far as to declare that you believe the opposite of what it says, you’re not Reformed Baptist. You’ve come a long way from the errors of standard modern Evangelicalism, so you are to be commended. However, the doctrines taught in the 1689 Confession are so strongly affirmed by Reformed Baptists that if you meet someone who tells you they are Reformed Baptist, they will expect you to be on the same page about all of it. If you go on to reveal your disagreement with a whole two paragraphs, they will be disappointed and feel like you’ve misled them.
1689 LBC, Ch. 29, §2: Those who do actually profess repentance towards God, faith in, and obedience to, our Lord Jesus Christ, are the only proper subjects of this ordinance. (Mark 16:16; Acts 8:36, 37; Acts 2:41; Acts 8:12; Acts 18:8)
Ch. 29, §4: Immersion, or dipping of the person in water, is necessary to the due administration of this ordinance. (Matthew 3:16; John 3:23)
But we would all agree that if a Presbyterian were to claim to be Reformed Baptist he would be exagerating at best. I have nothing against Presbyterians–I love Scotland and the history of the Scottish Reformation, and I am thankful for the legacy of the Confession of Faith that the Westminster divines hammered out over 1,163 meetings. But I am not Presbyterian when it comes to the topic of baptism. My point is, two paragraphs can be enough to distinguish between one and the other, and both Presbyterians and Reformed Baptists would consider the difference a very important one.
I am not of the persuasion that full subscription to the 1689 Confession should be a requirement for either leadership or membership in a Reformed church. I do believe that churches would do well to state in their materials that they believe the Confession to be an excellent summary of what is revealed to us in Scripture, but they would do better to point people to Scripture as the ultimate authority.
I think reformed churches should be lenient on intramural affairs. Whenever possible, Presbyterians, Baptists, Lutherans, the Dutch, should be able to fellowship together under the same banner. In the broader world outside the Reformed tradition, there is too much disunity over the more essential matters of salvation and the person of Christ. Those who are Reformed have so much in common, and they are so few in number that it is absolutely suicidal to divide over matters such as baptism and the Sabbath, or the metaphysical explanations of just what Jesus meant exactly when he said, “this is my body.” I’m not trying to start an ecumenical movement, but my prayer is that the Reformed family would find fellowship with one another and be a source of encouragement to each other rather than focusing on their differences.