What greater Knack could there be than the potential to change into any shape at will? The Exalted is marked with the secret Primordial Word for Luna. By activating this Knack they can transform their whole being into sentience and moonsilver.
   This Knack allows the Lunar to maintain a physical form, which is basically made out of Wyld Essence, while in the Wyld. In this shape they can hunt through the Wyld and engage in physical combat while within it. Pure moonsilver Warstriders can also accomplish this.
   Those who are individual and mindful enough to accept them are given Lunar Exaltation. They are given apparently limitless power to make themselves anything they desire. Their natural realm is the Wyld and it's their task to endlessly hunt it for Fair Folk who threaten Creation as Luna did before them.
   A full carapace of moonsilver can allow a warrior to maintain a physical form of sorts in the Wyld rather than having to transmute themselves into an abstract notion as the Lunars are capable of doing (turning their own identity into an abstract notion) to exist within the Wyld without their physical form being ruined. Maybe this is the true significance of their Spirit Shape. Ghosts, gods and demons can exist as Essence and naturally belong in other dimensions. Lunars can do the same thing. Their Spirit Shape is a Wyld Essence pattern formed expressing their own identity by the transmuting power of the Lunar Essence within them. They can exist in Creation in this form but naturally belong in the Wyld in it. It can exist as a coherent identity within the Wyld. The only thing other than a moonsilver form that can do so.