(1) It distinguishes gracefulness from beauty. The girdle properly belongs to the goddess, but the intrinsic glory of the goddess is not affected by wearing the girdle or not. Thus beauty need not be graceful, although gracefulness by its nature requires a connection to beauty.
(2) It indicates that graceful is transferable from the beauty to which it belongs. The girdle is something that Aphrodite can give to others; for instance, when Hera wishes to draw the love of Zeus, she borrows the girdle from Aphrodite. Only the goddess of beauty can bestow the girdle of gracefulness; but gracefulness can be given to other things. Thus the gracefulness that belongs to beauty may be thrown around something less beautiful, or even around something ugly; it still derives from some beauty, but it can make pleasing other things.
On the basis of these two considerations, Schiller draws the conclusion that gracefulness is movable beauty:
Grace is a movable beauty, a beauty that can appear in a subject by chance and disappear in the same way. In this it distinguishes itself from static beauty, which is necessarily granted along with the subject itself. Venus can remove her girdle and give it to Juno for a moment; her beauty could only be given in conjunction with her person. Without her girdle she is no longer the charming Venus; without beauty she is no longer Venus. (p. 125)
Anmuth ist eine bewegliche Schönheit; eine Schönheit nehmlich, die an ihrem Subjekte zufällig entstehen und eben so aufhören kann. Dadurch unterscheidet sie sich von der fixen Schönheit, die mit dem Subjekte selbst nothwendig gegeben ist. Ihren Gürtel kann Venus abnehmen und der Juno augenblicklich überlassen; ihre Schönheit würd sie nur mit ihrer Person weggeben können. Ohne ihren Gürtel ist sie nicht mehr die reizende Venus, ohne Schönheit ist sie nicht Venus mehr. (p. 172)
Yet we must be somewhat careful here. The girdle does not make someone merely apparently graceful; it gives them the quality of gracefulness, so that they do not merely seem but really are lovable. To receive gracefulness from a beautiful source is to receive an objective characteristic, not a mere extrinsic adornment. But, on the other side, transferring it does not change what the source originally is – Aphrodite does not become less beautiful by giving her girdle to Hera – nor does it change the nature of what receives it – it is a girdle Hera wears, not a change in Hera herself. The way Schiller puts it, this is not a natural effect, but a 'magical' (magisch) one: it does not affect natures, but changes what things are, nonetheless.
This is perhaps puzzling, an objective characteristic really received without lessening the giver or modifying the receiver herself. But we already know of something like this: movement (Bewegung), which is an objective characteristic, in some way transferable, and yet allows that what receives it be unchanged as to intrinsic features. Thus gracefulness is not only movable beauty in the sense of being transferable; it is movable beauty in the sense of being a beauty-movement, a beauty of movement.
Gracefulness can be transferred even to what is not beautiful; so what this means is that even the non-beautiful can have the possibility of having a beautiful manner of movement. On the other side, this explains why we can still distinguish between beauty and gracefulness. Beauty has a sort of necessity to it: Aphrodite is beautiful by nature. But gracefulness has a contingency to it. If something is necessary, we don't call it graceful, although it may be beautiful; but something graceful is something that is a sort of extension that can be or not be.
Schiller, however, notes that the Greeks tended to associate gracefulness not with every kind of contingent movement, but only with human kinds. Now, to be sure, we can always extend this by figure of speech, but in a proper sense does all gracefulness have to be human as the Greeks tended to think? Schiller is inclined to say so, and suggests that gracefulness properly requires movement that is expressive of moral (moralischer) sentiments. It is an expression of soul, and thus he draws his final conclusion from the myth: “Grace is a beauty not granted by nature, but brought forth by the subject itself” (p. 127); Anmuth ist eine Schönheit, die nicht von der Natur gegeben, sondern, von dem Subjekte selbst hervorgebracht wird (p. 175).
This is all, of course, simply drawing out an allegory from a myth, but Schiller goes on in the rest of the essay to argue that this myth anticipates and reveals what philosophical reason can also prove.
Quotations from Schiller's “On Grace and Dignity” in Its Cultural Context, Curran and Fricker, eds., Curran, tr., Camden House (Rochester, NY: 2005).