This verse is as if the Apostle said, in view of this denial of the resurrection which had gotten in among the Corinthians, "Well, since the object in baptism is death-for we are baptized 'with a view' to it-the very fact of our baptism marks us out for death. What fools you are then to have become Christians if, when the initiatory ordinance points to death, there is no resurrection."
As in a "forlorn hope" men step forward to fill up the ranks of those cut down in death, so was the place of those who "are baptized for [or over] the dead," thus filling up the places, as it were, of those, perhaps, who were martyred for Christ's sake. "Now," he goes on, as it were, "if dead persons do not rise at all, it would be folly to own practically what our baptism implies."
Look at the scope of the chapter and the arguments of the Apostle against what was among them at Corinth, as well as at the objective character of baptism as having death in view, and you will see the force of the verse more distinctly.