The two weapons
Midway through the book, it is revealed that the two weapons, Heaven Sword and Dragon Saber, are actually made from a single sword, Xuan-Tie-Jian, which Yang Guo wielded in the prequel (set nearly 100 years ago), The Return of the Condor Heroes. The great sword belonged to Dugu Qiu Bai, a great martial arts hero whose skills were unmatched under the heavens. Yang Guo came upon the sword while he was recovering from the loveless poison and the loss of his arm.
Later, when Yang Guo and his master/wife, Xiaolongnü left Xiangyang, he left the sword with Guo Jing and Huang Rong. It was said that the sword was melted, special steel material was added and made into the Heaven Sword and the Dragon Sabre. Hidden within the Dragon Sabre was the military textbook (Wu Mu Yi Shu) written by the late great Sung Dynasty general Yue Fei;
similarly, hidden within the Heaven Sword was a scroll detailing the powerful martial art Jiu-Yin-Zhen-Jing and (legends told that Guo Jing wrote the Dragon Subduing Palms or Xiang Long Shi Ba Zhang manual along with Jiu-Yin-Zhen-Jing). The former was given to Guo Jing and Huang Rong's son while the latter was bestowed upon their youngest daughter, Guo Xiang who was Yang Guo's favorite and founder of the Emei Sect.
The content of the hidden book and scroll, plus the fact that the two weapons can only be broken (thereby revealing said book and scroll) when used against each other, was the source of the claim that whoever possessed the sword will be "untouchable" and whoever possessed the sabre will rule "all under heaven".
The secret of the weapons was passed down via (and only through) the leaders of the Emei Sect. Zhou Ziruo was the latest leader of the sect, and about half-way into the novel, she managed to obtain the two weapons through her scheming and deception.
The two weapons analogy: In the Chinese culture, the dragon is considered a king, which probably why many of the TV adaptions gave the sabre a golden-copper color. The Dragon Slaying Sabre means to kill the king (which in this case is the Mongolian ruler). However, dragons can get out of control and become tyrants. The Heavenly Sword is Heaven. Only Heaven is the true and only authority in choosing a ruler and dethroning him. At the end, the Dragon Slaying Sabre is destroyed by the Power of Heaven.
Woow, i didnt know these.