Baptism

Where did baptism come from?  Why are people so ready to be immersed in water without asking questions?  Why a river?  Why not a lake or ocean?  Was it just taking a bath to purify oneself?  Christians believe that baptism is used to purify the person from sin or wash away their sins, but Jesus, who was supposedly without sin, insisted on John the Baptist baptizing him.  The Mayans and Native Americans baptized with a ritual very similar to what the conquistadors were used to seeing.  The patriarch religions stole everything.  Baptism is just one more block I will remove from the wall of lies.