Pentecost took place before Paul had written any of his teaching about baptism in Romans, Galatians, 1 Corinthians, or any of his other books. In fact, it took place some time before he was even saved.
When, therefore, after his message at Pentecost, Peter responded to his hearers’ question about what they should do (Acts 2:37) by saying, “Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost” (2:38), what baptism did he have in mind and what was his understanding of its significance?
Moreover, what understanding of baptism and its significance did those people have who heard his word, gladly received it, and were baptized (2:41)?
If these who were baptized were given the truths by Peter (as perhaps part of the information that 2:40 summarizes) that Paul teaches in Romans 6, Galatians 3, etc., then what Paul wrote many years after Pentecost in those passages was not new essential revelation to the Church at large about the fundamental significance of baptism. On the other hand, if what he wrote there was new essential revelation about the fundamental significance of baptism, then how were these who believed and were baptized at Pentecost baptized without that information?
Scripture provides no hint that these who were baptized at Pentecost had an incomplete understanding of anything essential about the importance and significance of baptism. Nor does it say anything about a vast number of believers being re-baptized once Paul came on the scene and wrote what he did in his Epistles about baptism (e.g., Romans 6). What, therefore, should we conclude about the importance of giving the Pauline epistolary teaching on baptism that we now have to new believers in our day prior to their being baptized?
Peter preached that those who would repent and be baptized would receive the gift of the Holy Spirit (2:38). Incredibly, Luke, however, does not say that those who gladly received his word received the Spirit. Instead, he only comments that they were baptized and added to those who were already believers prior to Pentecost (2:41). Why does Luke not say anything about their receiving the Spirit in relation to their being baptized after having received the message?