Commentary on the Dragon, by Sajius, is a commentary on The Karaethon Cycle.  Sajius claimed that the phrase "He shall hold a blade of light in his hands, and the three shall be one." referred to the unification of three nations. Min believed that interpretation is incorrect, and that the passage has something to do with the use of Callandor.
During the Last Battle, Rand, Moiraine, and Nynaeve use Callandor to pull Moridin into their circle. Using saidin, saidar, and the True Power, Rand creates a new seal on the Dark One's Prison, thus achieving victory at Tarmon Gai'don.