The title refers to a motto I've seen used by the US military forces, usually in regards to firearms usage, meaning that whatever weapon winds up in your hands, it is your mental attitude that matters most. YOU are the weapon. I've written about this before and it is my particular bent towards interpreting Medieval Martial Arts. Armizare, Fiore's art, is a weapon-based Archetype System. By that I mean that each of the weapons you are instructed in, dagger, one-handed sword, longsword, spear, & poleaxe, acts as an archetype for that particular "class" of weapons. For instance, the longsword can, in practical terms, be a stand-in for any two or one handed ~4' long weapon. This is my answer to the question of why we don't see maces, single-handed axes, or warhammers represented in the manuscripts - they are already there, just in archetypal form. The Germans have the messer material, Fiorists have the sword in one hand and mounted sword sections.
Now, the archetypes are not a perfect analogue across the board. For instance, in the messer/arming sword you have that lovely little piece of metal that protects the hand. Hand guards, to my knowledge, are not really that common on maces, hammers or axes, so any technique where you come into Kron/Frontale (and if you don't have an armoured gauntlet on) life will be not that happy for you. The medieval arts are not the only martial arts to take this approach - in my limited knowledge of them, the arts of Escrima and Kali operate on a similar model - what is done with the sword is done with the stick is done with the knife is done with empty hands. Armizare rolls the same way - the Remedy of the 1st Master of Dagger (at least how I interpret it) is similar to the Remedy of the 1st Master of Longsword. The Breaking of the Point is done almost the exact same way across all weapons. It's beautiful.
The thing I love about the mindset of "One Mind, Any Weapon" is that is applies to anything and everything. Think of all the ads you've seen for DVDs or books that will teach you to use improvised weapons - magazines, pens, books, backpacks, etc. All of that is covered in "One Mind, Any Weapon".
Try this as an exercise - Look around the room you're in and pick the first 3 objects that catch your eye. Utilizing whatever art(s) you're trained in, figure out a couple ways you could use that object to defend yourself. It's kinda fun, in a paranoid sort of way ;)