I believe Scripture teaches the importance of baptism. Jesus’ commission in Matthew 28:19–20 identifies its importance. Jesus commanded His disciples (and us by implication) to make disciples of all nations by teaching them and by baptizing them in the name of the Father, Son, and Holy Spirit. From his command, we can infer that baptism is a required step of obedience for a disciple, that is, a person who is already saved.
Baptism is not, however, a required step to receive salvation. To help people see this, you have to show them that the Bible teaches that faith alone is necessary for salvation. Once you demonstrate that faith alone is necessary for salvation, then it logically follows that baptism is not necessary for salvation.
Romans 3:21–5:11 and Galatians 2–5 are the two places in the NT designed to teach us what is necessary for salvation. Paul argues that “a man is justified by faith apart from works of the Law” (Rom 3:28 NASB) He expands this argument in Romans 4 by demonstrating that both Abraham and David were saved by faith alone (Rom 4:1–11). Paul’s opponents were arguing that faith plus circumcision were the necessary conditions for salvation.
This is the same argument used by those teaching baptismal regeneration when they say faith plus baptism is necessary for salvation. Paul’s point is that salvation has always been by faith alone and nothing else, including circumcision. Since Abraham and David serve as examples of what is necessary for NT believers to be saved, we can safely say that baptism is not a necessary condition for salvation.
Paul also develops this argument in Galatians 3. The Galatians received the Spirit by the hearing of faith (Gal 3:2). Later in the chapter, Paul argues from Habakkuk 2:4—“The just shall live by faith”—that faith alone is the basis for justification (Gal 3:11).
Admittedly the phrase “saved by faith alone” is not found in Scripture. However, neither is the term “trinity.” Nonetheless, both are not only legitimate inferences, but I would argue that they are both necessary inferences from Scripture.
Several biblical stories support this conclusion. In all the following cases, people were declared justified or saved, without any indication that they were baptized: the repentant tax collector (Luke 19:8–10), the woman at the well (John 4:1–42), and the thief on the cross (Luke 23:43). There are more examples like this, but I think this is sufficient to make the point. Key point: don’t use these stories without first arguing for justification by faith alone; otherwise, you are just arguing from silence without providing positive proof for your position.
On the other side of this issue, the most common error that baptismal regenerationists make is the fallacy of the negative inference. For example, “if you were born in the US and are a resident of Ohio, then you are a US citizen,” does not imply “if you were born in the US but are not a resident of Ohio, then you are not a US citizen.”
Some baptismal regenerationists read Mark 16:16, “He that believeth and is baptized shall be saved,” and wrongly infer the negative, ”If you believe but are not baptized, you will not be saved.” This conclusion is a classic example of the negative inference fallacy. Some commit the same fallacy regarding Acts 2:38 and 1 Peter 3:21.
In conclusion, I'd like to highlight the fact that dealing with theological errors requires a good working knowledge of logic. This is an important reason why the study of logic ought to be a part of every child’s education, whether formally or informally.