The weapon represents a warrior's spirit. Even when the warrior dies, the weapon remains imbued with the warrior's will and lifelong experience.
Thus, it contain a warrior's soul and power.
To help Carso increase his power, Master Soga needs a good deal of weapons. Collect some for him. He'll reward you; it'll surely be worth your while.
The Tempus Lizards drawn by Carso's power have become too numerous to control. Soga doesn't need unreliable servants...