Garp the Hero envies how Roger and Whitebeard died and wishes to die in the same way. The World Government intended to have Roger be publicly executed to discourage piracy, but his last words had the opposite impact. He stated that anyone who can find his treasure can claim it. As such, this made Roger single-handedly responsible for starting the Golden Age of Pirates.
Whitebeard was widely known as the “Strongest Man in the World” and, after Gol D. Roger’s death, the “Man Closest to One Piece”.
Before dying, he proclaimed to the Marines that the discovery of the One Piece would result in a grand battle that engulfed the entire world, declaring that the One Piece did indeed exist. He then died after having been slashed and stabbed 267 times, shot by 152 bullets, and hit by 46 cannonballs. Even in death, however, he remained standing, and did not have a single wound on his back. Whitebeard’s dying words provoked the New Age of piracy and inspired countless pirates to voyage to the New World, just as Gol D. Roger did.
Kaido met his demise at Luffy’s hands. Kaido believed only Joy Boy would bring about his demise.
Dark King Silvers Rayleigh trained Luffy because he believed Luffy is the one. The prophecy ties all of the events to a particular time. And the time is now..
All the old geezers have been waiting for this time and this has already started with the defeat of Kaido in Wano.
Please note that Garp has been to the Fishman Island. Garp is aware that the time is now.
Garp as a Marine [Marine Hero] who is aware of the prophecy, is the one to recognize Blackbeard.
Garp will die honorably and like Whitebeard he will say that Blackbeard is not the one Roger is waiting for.
Since Garp will meet his demise at Blackbeard’s territory, Blackbeard will be named as the suggested Pirate King.