Baptism for the Dead in 1 Corinthians 15:29? WHY?

Otherwise, what will those do who are baptized for the dead? 

If the dead are not raised at all, 

why then are they baptized for them? 

1 Corinthians 15:29 

"Numerous explanations have been offered for this verse,....Mormonism claimed that this verse supports their view of baptism for the dead. In their practice, individuals go to their local Mormon temple, dress appropriately for a baptism, representatively adopt the name of a person who has died, and then the Mormon is baptized in water for that deceased person. 

But, the Mormons are incorrect. They have usurped this verse and taken it out of context.

In verses 1-19, the fact of Christ's resurrection is detailed by Paul. Beginning in verse 20 and going through verse 23, Paul speaks about the order of the resurrection. Christ was the first one raised--in a glorified body--and next will be those who are His at His return. 
Verses 24-29 then mention Christ's reign and the abolition of death. This is when this controversial verse occurs: "Otherwise, what will those do who are baptized for the dead? If the dead are not raised at all, why then are they baptized for them?"

Just north of Corinth was a city named Eleusis. This was the location of a pagan religion where baptism in the sea was practiced to guarantee a good afterlife. This religion was mentioned by Homer in Hymn to Demeter 478-79.
 The Corinthians were known to be heavily influenced by other customs. 
It is probable that the Corinthians were being influenced by the religious practices found at Eleusis where baptism for the dead was practiced.

Paul used this example from the pagans when he said, " . . . if the dead are not raised, then why are they baptized for the dead?" Paul did not say we.
This is significant because the Christian church was not practicing baptism for the dead, but the pagans were.
Paul's point was simple. The resurrection is a reality. It is going to happen when Jesus returns. Even the pagans believe in the resurrection, otherwise, why would they baptize for the dead?" CARM

 ELEUSINIAN MYSTERIES AND RITES

  "Eunapius, in Vita Maxim, says : "I rmLj not tell the name of him who was then hierophant, for it was he who initiated me." The manner in which the name was committed to the sea was either by the immersion of the bearer or by writing the name on a leaden tablet, which was cast into the sea.

 The Eleusinian Mysteries seem to have constituted the most vital portion of the Attic religion, and always to have retained something of awe and solemnity. They were not known outside Attica until the time of the Median wars, when they spread to the Greek colonies in Asia as part of the constitution of the daughter states, w^here the cult seems to have exercised a considerable influence both on the populace and on the philosophers. 
THE Eleusinian Mysteries, observed by nearly all Greeks, but particularly by the Athenians, were celebrated .yearly at Eleusis, though in the earlier annals of their history they were celebrated once in every three years only,....."
 From THE ELEUSINIAN MYSTERIES & RITES, DUDLEY WRIGHT