Why does a Blacksmith bring swords to Rhysand, and what is decided about the swords?

The blacksmith that Cassian and Nesta visited brings a sword, a dagger, and a longer great sword to Rhysand. He says that they are cursed. Cassian reveals that Nesta hammered the blades. Amren decides that Nesta put her power into the swords and has created a new Trove. Amren warns Rhysand not to unsheath the weapons, and she thinks that Nesta should not learn what has happened.