In Japanese culture, Courage (Will, actually), Wisdom, and Power were seen as a trinity of sorts, and makes it's way into Japanese popculture like CT and heck, even Zelda's Triforce, and other examples in video games and anime. The Japanese believe that without one of these three traits, the other two are meaningless. Power without the Wisdom and Will to use it are worthless. Wisdom without the Power and Will to use it is worthless, and Will without Power or Wisdom to use it is meaningless.
Perhaps Melchior intended the Masamune to have the Power, Wisdom, and Will to be used as a holy weapon to create, and never strike down the innocent (See actual Masamune myth). Without Doreen, however, the Sword is merely Power and Wisdom with no Will. Thus, the Masamune draws strength from the will of it's bearer. This ultimately led to it's corruption, as we know, and Doreen created the Mastermune, the Ultimate Weapon Melchior invisioned.