According to the two oldest sources on the life of Jesus…the Gospel of Mark and the hypothetical Q Source(s) theoretically preserved in the Gospels of Matthew and Luke…the very first thing that happens is Jesus’s baptism by John the Baptist. The existence of this apocalyptic preacher, often thought of as the forerunner of Jesus, is independently confirmed by Josephus later in the first century.
This has led many scholars to believe that Jesus was a disciple of the Baptizer before starting his own ministry. The baptism by John is also considered one of only two events that nearly every scholar believes actually happened in Jesus’s life (the other being the crucifixion). Reasons for believing this is simple: if followers of Jesus really believed he was god, why would early Christians have included stories that made him appear subservient to John?
However, if the synoptic Gospels are any indication, Jesus’s theology would have differed significantly from John’s. John seemingly advocated for an ascetic lifestyle that lacked any hint of universalism that characterized Jesus’s ministry. At some point, it would appear, there was a philosophical break between John and Jesus, possibly caused by John’s execution by Herod Antipas (an event also recorded by Josephus). This break could have been the impetus for Jesus’s ministry.
In my view, Jesus’s connections to John’s movement would have been too well known for early Christian writers to conceal. Therefore (much like the crucifixion) John the Baptist was integrated into Christian theology…as a “forerunner” to Jesus…to cover up what would have otherwise been an embarrassment.
The above link is from biblical scholar James Tabor, formerly of UNC Charlotte. I’ve mentioned previously that I sometimes find him a little gullible, but he usually makes interesting arguments. In the article, looking at a Hebrew translation of the Gospel of Matthew, Tabor observes that Jesus is, in fact, seen as lesser than John the Baptist. While ancient historians did state that Matthew was originally composed in Hebrew, insofar as I am aware, the Gospels that we have today were seemingly written entirely in Greek, meaning that these historians were mistaken in their belief. For this reason, I don’t put too much weight into Tabor’s claims. BUT, I add it here to highlight how early Christianity was far from uniform in its theology. In fact, it would look quite alien compared to contemporary Christianity.