en_tn_lite_do_not_use/1co/15/29.md

Or else what will those do who are baptized for the dead?

"Otherwise it would be useless for Christians to receive baptism for the dead."

If the dead are not raised at all, why are they baptized for them?

Apparently some people, probably some members of the church in Corinth, were being baptized for the dead. Paul infers that those people did so because they believed that the dead would be raised.