Callandor, one of the most powerful sa'angreal, was held deep inside the Stone of Tear; the Heart of the Stone. There were weaves made of both saidin and saidar meant to prevent anyone from ever touching Callandor.
“Cautiously, she reached out with the Power, probing at whatever held and shielded the sword. Her probed touched – something – and stopped. She could sense which of the Five Powers had been used here. Air, fire and Spirit. She could trace the intricate weaves made by saidar, set with a strength that amazed her. There were gaps in the weave, spaces her probe should slide through. When she tried, it was like fighting the strongest part of the weave head on. It hit her then that she was trying to force a way through and she let her probe vanish. Half that wall had been woven using saidar, the other half, the part she could not sense or touch, had been made with saidin. That was not it, exactly – the wall was all one piece – but it was close enough”
(Egwene The Dragon Reborn, Chapter 27).
When Perrin visits the sword in the Stone he can't get close to the sword
“Huge columns of polished redstone surrounded the open space where he stood, beneath a domed ceiling fifty paces or more above his head. He and another man as big could not have encircled one of these columns with their arms. The floor was paved with great slabs of pale grey stone, hard yet worn by countless generations of feet. And centered beneath the dome was the reason why all the feet had come to this chamber. A sword, hanging hilt down in the air, apparently without support, seemingly where anyone could reach out and take it. It revolved slowly, as if some breath of air caught it. Yet it was not really a sword. It seemed made of glass, or perhaps crystal, blade and hilt and crossguard, catching such light as there was and shattering it into a thousand glass glitters and flashes. ...A foot from the shining sword, his hand splayed out against empty air as if it had touched stone”
(Perrin, The Dragon Reborn, Chapter 5). Emphasis mine
However, when Rand fights Ba'alzamon after Moiraine kills Be'lal, he throws himself towards Callandor and seizes the sword (The Dragon Reborn: Chapter 55). He experiences no resistance in trying to get at the sword.
This means that the weaves were set in place to prevent anyone except the Dragon from touching the sword.
Even further, the protection around and inside the Stone of Tear was immense. The Defenders of the Stone's sole purpose was to protect the Stone and prevent anyone, even the Dragon, from gaining access to Callandor.
Once the Dragon touched the sword the weaves were broken, the prophecies were fulfilled.
In The Shadow Rising: Chapter 21, Rand drives the sword into the floor of the Heart of the Stone, further fulfilling the part of The Karaethon Cycle:
Into the heart he thrusts his sword
into the heart, to hold their hearts
Who draws it out shall follow after
What hand can grasp that fearful blade
and challenging anyone to take the sword if they dare while he is gone. Later, when questioned by Moiraine and Egwene, Rand says he was merely fulfilling the prophecies and tells them about the trap he has set with the One Power should anyone try to take it. (The Shadow Rising: Chapter 21)
Path of Daggers content:
Rand sends Narishma to get the sword, obviously he told Narishma how to unravel the traps Rand placed around the sword. (Path of Daggers, Chapter 14).
