Baptism by immersion in water did not originate with Christians, or as many suppose with John the Baptist. The Jews had practiced baptism as a traditional act of purification and initiation long before the coming of the Messiah.
As a Jew, John the Baptist was the son of a Levite priest, Zechariah, and John's mother Elizabeth, also a Levite, was a relative of Mary. Thus, this well-known religious character would have been well familiar with the practice before he was sent to baptize, proclaiming "Repent, for the kingdom of heaven is at hand."
I wonder if there is a significance in that there is no Biblical record of John's own baptism?
Predating John, the ancient Levite priests executed a symbolic cleansing in water, involving being dipped, or in fact dipping oneself in the Jordan seven times.
The belief was that It was not the water that healed or forgave sins, but through an act of obedience and faith whereby God made the individual “clean.”
As Christianity evolved this took on a more extended and significant meaning. By being baptized into Christ, one is by the act of immersion (burial !!), being baptized into his death and resurrection. One can easily now discern the distinction in the phrase “To cross over the Jordan.”
Maybe the truth of it all is that we’re just too fearful to give our faith enough space to realize that this precariously thin path that led us to the end of this life is dwarfed to obscurity by the infinitely vast freeway that begins immediately on the other side.