Although most likely there is a deeper message to metamorphoses, on the surface it teaches a worldview of mediocrity. The beautiful women all ended up raped by the male gods, and despised by the female gods. Those who did excellently were attacked and destroyed. It also teaches a worldview of submission to the powers that be. Those who refused to submit to the gods suffered. Those who were prideful, and thought that their deeds and accomplishments made them equal to the gods were soon disabused of that notion by a display of the might of the gods.
By portraying beautiful women as the objects of the gods, Metamorphoses is teaching that beauty is not to be desired. It teaches that beauty is, in fact, something that should be avoided, because when the gods desire a mortal, chaos results, usually including great loss to the object of that desire. So, following this to its logical end, beauty leads to pain.
In the same way, excellence is seen as resulting in suffering. Arachne is truly excellent at weaving. When she contested with Athena she did not loose. That gained her nothing, however, in the long run. In the end her excellence destroyed her. Arguably it was her arrogance, but it seems that since not even Athena could best her, her arrogance should have been forgivable. What destroyed her was that she was at least as good as the goddess, if not better.
When those who refuse to submit and are prideful are attacked by the gods, that teaches that those qualities lead to great pain by showing pain as a result of pride and insurrection. For example, Niobe was very prideful, and the gods smote her mightily. Penthius is an example of insurrection against the gods. He denied the deity of Bacchus, and threatened him with bodily harm. This resulted in him getting his head ripped off by his mother as she celebrated Bacchus. Insurrection equals death and pain. Pride equals suffering.
These stories are able to shape the worldviews the simple who read them because they are stories. Stories reach into our souls and allow us to think outside the box without hurting our minds, because they can be read without engaging our minds at all. Because we tend to suspend value judgments when we read myths, we are unable to combat the values presented. When we have no defense against something, it will shape us.