Did people know what John the Baptist was talking about at first when he came and said “repent and be baptized”? Is there a precedent for baptism in the Old Testament? Or would people have looked at each other and scratched their heads when he first started preaching baptism? I realize that it’s a symbol of the crossing of the Jordan, the Red Sea, and of the Flood, but was baptism ever practiced as a ritual before John?
If you do a word search on the word wash in the Old Testament – you can see my results by clicking here – you’ll see that the Old Testament is full of references to ritual washing. Of particular note is Elisha’s instructions to Naaman in 2 Kings 5 to ritually wash himself in the Jordan as a cure for leprosy (a biblical figure of sin).
Also, it is a noteworthy part of Jewish tradition that the Jewish people, from ancient times to the present, have had ritual baths known as mikvahs. (Indeed, ancient *mikvah *sites have been found by archaeologists in the Holy Land.) The mikvah was commanded under Jewish law to cleanse a person of ritual impurity (e.g., a woman would go to a mikvah after her period of ritual impurity during and after menstruation).
So, yes, it is likely that the people to whom John the Baptist preached had a good idea of what he was referring to when he instructed them to be cleansed of their sins in the River Jordan (which, because it is a natural body of water, could itself have possibly been used as a mikvah).