When Jadzia Dax died, everyone mourned.
Usually, in fiction, a popular character that has died can be brought back as an unknown identical twin of the dead character, as a clone of the deceased character, or the character is a descendant of that character from a separate timeline but looks identical to the dead character.
However, the memories of Jadzia, as well as the memories of all of Dax's previous hosts have been transferred to Ezri, the new host of the Dax symbiont. Those memories will remain in existence as long as the Dax symbiont remains alive.
This resurrection is different. You will have to traverse the prologue, and the early chapters in order to find out how this resurrection is achieved. Rest assured that the journey is worth it. Happy travels, Morgan Sinclair