One of the ways in which I moved from partial to fully biblical (that is, Catholic) faith was by discovering that my little dorm group was wrong about baptism. In the early Church, to believe and profess your faith and to be baptised were the same thing. If you believed, you sought baptism and if you were baptised, you were, ipso facto, a believer. Controversies dating from a millennium-and-a-half after the time of the New Testament still have many Christians today splitting hairs over ‘water baptism’ vs. ‘Spirit baptism’ or vs. ‘profession of faith’, but none of that would have been intelligible to the authors and original readers of the New Testament. What they took for granted was not the distinction between baptism in water and the gift of the Spirit or the profession of faith in Jesus, but the identity of all three of these things. To ask them to choose between these three things was like asking them which blade on the scissors does the cutting. It was a nonsense question.
Profession-of-Faith-and-Baptism was how you both entered the Body of Christ and how God the Father gave you his Spirit through Christ the Son. You were “born again of water and the Spirit” (John 3:5). Accordingly, with the sole exception of the Good Thief (who is, tellingly, understood by the early Church as having been baptised in blood, not water), every convert in the New Testament is baptised when they believe the preaching of the apostles whom Jesus commanded:
Go therefore and make disciples of all nations, baptising them in the name of the Father and of the Son and of the Holy Spirit, teaching them to observe all that I have commanded you.” (Matthew 28:19-20)