Legend as I know it.

Many centuries ago, a wizard of the Old Ways saw the arrival of a new faith. Seeing the followers of this new faith doing horrible things to others like him, the wizard decided to use their faith against them. He had seven distinct swords made and endowed each with one of their deadly "sins". To guard each sword, the wizard chose each of his seven daughters to counter each one. One daughter per sword, he chose them to hold the sword that was opposite their own personalities. Those seven sisters guarded and used the swords until their deaths. As each sister died, the sword vanished to later return in the hand of another young girl who had the same kind of personality as the sister who had last held it. These girls felt as if they were sisters even though they had never met before. It was this way for five generations.
Eventually, kings sought the swords for the powers they held. One king commissioned a team of wizards to make a keeper for all of the swords so they would not vanish when their guardians were killed. They succeeded. Imprisoning the guardians, the king forced the sisters to impale a magical sword holder with each of the swords. When all seven were encased, the sisters were slaughtered.
The king's victory was short lived. With all seven swords together and no guardians to balance them, their "sins" radiated out and permeated the castle and surrounding area. The king died at the hand of his own son. This same son shattered the holder and watched all seven vanish before his eyes, much to his dismay.
The whole set would not be together for another four generations. The set of circumstances that brought them and the girls holding them is lost to history. During their time, the area was in harmony and peace. But, again, they would be killed and the swords lost due to a king's pride.
For the past six generations, only two or three swords have been brought together, usually magically encased or otherwise imprisoned and usually in a monastery. Personally, I've only heard of rumors that Lust and Greed are is a remote monastery where the vows of poverty and chastity are the only things keeping the monks from succumbing to the power of the swords.