When John the Baptist baptized Jesus, what would the baptismal formula have been? “Father, Son, and Holy Spirit” wasn’t used until the 2nd Century.
THE RELIGION GUY’S ANSWER:
Even a highly skeptical scholar like John Dominic Crossan considers it historical fact that Jesus inaugurated his public ministry with baptism performed by his cousin John the Baptist, who was “preaching in the wilderness.” There’s also wide agreement that John would have used full immersion in the waters of the Jordan River (those loud amens you hear are coming from Baptists). But as for what words John recited, the Bible doesn’t say though, yes, it doesn’t seem plausible he would have spoken Christianity’s familiar invocation of the triune God that Gerald quotes.
The Acts of the Apostles depicts three baptisms during the earliest phase of the Christian movement, each performed in the name of Jesus and not the Trinity (which is the practice of modern-day “Oneness” Pentecostals). However, the Gospel of Matthew, written in the same time frame as Acts, suggests belief in the three divine persons in the Trinity in its account of Jesus’ baptism (3:13-17, paralleled in Mark 1 and Luke 3). As Dale Allison comments, “the Son is baptized, the Father speaks, and the Spirit descends.” Then the Trinity becomes explicit in Matthew 28:19 as Jesus directs his followers to make disciples, “baptizing them in the name of the Father and of the Son and of the Holy Spirit.”
So invocation of the Trinity quickly emerged in the 1st Century as a permanent feature of Christian baptism.