What does St. Paul mean by baptism for the dead in 1 Corinthians 15:29?

Paul says, otherwise what shall they do who are baptized for the dead, if the dead rise not at all? Why then are they baptized for them? The word for are baptized is a present participle here without regard to time, referring to anyone baptized in the past or the future, which includes all the Corinthians and all Christians. Paul emphasizes baptism because it is this very sacrament that connects every Christian with death and resurrection, as he explains in Romans 6: we are baptized into Christ's death so that we will be alive with Him in His resurrection. It does not mean the baptism of one person transmits some benefit to another; with the Greek article included, baptized for the dead refers to one group, the baptized Christians who have died in the hope of being resurrected. The hope of resurrection after death is also why the living seek baptism. So the point is simple: these Corinthians were watching their brethren die every day and wondering what guarantee they had of seeing them again, and Paul says, if there is no resurrection, why are the living even being baptized? The living are baptized precisely because of the hope that those who have died will be raised. There is no big mystery here; people try to make one out of it, but that is not Paul.