Jarul said that the world must be cut to parts someday? I mean..again? What it may mean?
He probably means the world will continue to separate further to what was told because the world is already separated as we already know. Gunko said the world will be destroyed one day, so this separation is the result from this third destruction that will happen in the future.
The world was supposed to be completely destroyed during the void century but Joyboy stopped it, he hid the ancient weapon away to protect it from Imu or Davy Jones. The CDs were constructing the 4 wolf bridges since the void century and was started around the destruction of void century. So Imu has been preparing using these bridges for the complete destruction, the entire world sink into the ocean. However that doesn't match with what Jarul said. So there could be several people trying to destroy the world based on the difference of ideology. Imu wanted it this way, DDJ wanted another way, and Joyboy wanted the other. In the end, one of them will succeed. By that means the one foretold in the mural.
Many have guessed that Red Line will be destroyed. Destroying it would mean catastrophic to the world. My wild guess is the Red Line is a binding that held the world together like a rubber band tying up several pieces that made up a sphere which means the Earth. So destroying it will set the world loose into several parts.