Lustration 

Lustration, also known as Baptism, seems to mean purification by Water.   Most ancient nations used this practice during initiation of a person into the Mysteries. Lustration was practiced by the Hebrews, the Greeks, and the Romans. It was more common with the Romans than with the Greeks. The Romans used lustration to secure the blessing of the gods. (See "The History of Freemasonry" by Mackey page 279)

Lustration, or cleansing by Water, was usually done to a person just before they were initiated into the Mysteries. It seems to have been, and still seems to be, symbolic of the purification of the heart to receive the Mysteries.

Lustration is practiced by some Religions, including Christianity, under the name of Baptism.

Did Christianity come up with the idea of Baptism (Lustration) by Water from the ancient Mystery Religions which were in existence long before Christianity?  Since so many of the ideas and beliefs of Christianity have come from the Pagans, why not this one?

Even though this has been practiced for a long time is still seems like a rather worthless ritual.

I do not understand why the Supreme Being would require that a person be immersed in Water or sprinkled with Water by a priest in order to be 'saved' and thus become perhaps eligible for 'heaven'.  God may wish people to be clean but they should be able to bathe and clean themselves alone.

It does not seem a whole lot different to me than taking a bath or shower, or even going swimming.  Would getting in a swimming pool with a priest accomplish the same thing?

At one time most Europeans deemed bathing in water to be unhealthy.  Of course since they dumped their sewage into the rivers this may have been at least somewhat true.