There is, in any case, no doubt that the Aesthetic Letters were enormously influential. Frank's interpretation of Schiller's text is accurate and intriguing.
From Rousseau come some back-to-nature comments about the dangers that civilization poses to spontaneity.
The self-sacrifice of Leonidas at Thermopylae, for instance, elicits both a positive moral and a positive aesthetic judgment: Judged from a moral perspective, this action portrays for me the moral law being carried out in complete contradiction of instinct.
Thus, we come up short against a sublime object physically, but we elevate ourselves above it morally, namely, through ideas. It is particularly difficult to summarize and comment on Manfred Frank's quite dense and well worth reading "Schiller's Aesthetics between Kant and Schelling".
The expectations are consistently disappointed, but the intoxication remains. Schiller develops a general ontology of freedom that comprises not only the sphere of human action but also the realm of things, of natural as well as of cultural entities.
But complete self-creation isn't up for debate, anyway, when we speak of freedom.
It is the same with the good: a virtual morality is not moral. These patterns developed in the course of evolution in alignment with the world. The critical Kant, however, began elaborating the logic of dualism.