The universe is not treated as an admirable cosmos, with the explicit purpose of providing moral and intellectual support to the citizens, in the way Plato is going to state in the Timaeus and in the Laws.
Although these presuppositions may appear to be self-evident, most of the time, human beings are aware of them only implicitly, because many individuals simply lead their lives in accordance with pre-established standards and values that are, under normal circumstances, not objects of reflection.
And the Beautiful, and the Good?
It is therefore a matter of conjecture whether Plato himself held any positive views while he composed one aporetic dialogue after the other. Because Plato's Form of the Good does not explain events in the physical world, humans have no reason to believe that the Form of the Good exists and the Form of the Good is thereby irrelevant to human ethics.
Humans are compelled to pursue the good, but no one can hope to do this successfully without philosophical reasoning. In the Republic, by contrast, the soul itself becomes the source of the appetites and desires.
Nowadays, we might compare the Form of the Good to laws of nature, though this is not fully satisfying, since the Form of the Good is not particular law of nature, but the reason why there are laws at all.
Hence, it is clear that justice is a good state of the soul that makes its possessor happy, and injustice is its opposite. The message of the the Symposium and the Phaedrus is therefore two-pronged. This is what the scala amoris is all about.