Pericles described the School of Hellas to his audience and today we study Greek art as a reflection of the qualities enumerated by Pericles. Why?
This question refers to Pericles' Funeral Oration in Book 2 of Thucydides' History of the Peloponnesian War. Thucydides makes Pericles say that Athens, because of her manifold excellent qualities, is "the school of Hellas" (i.e., Greece). Thus, the public and private practices of the Athenians can be instructive to all Greeks.
When Thucydides wrote his History, Pericles had been dead for several years, but the monuments to which Thucydides makes Pericles refer in his speech were still visible to anyone who visited Athens. Some of these monuments can still be seen today (although sadly in a state of decay).
The most prominent monuments, which were part of Pericles' building programme, are the Parthenon, the Propylaea, the Temple of Athena Nike, and the Erechtheum (although this last building was started and finished after Pericles' death). These buildings (and the sculptures that adorned them) are still considered the pinnacle of Greek art.
Because one of the functions of the Periclean building programme was to recall Athenian victories over the Persians (i.e., barbarians), some of the sculpture on the Parthenon depicts Greeks battling with barbarians (e.g., Lapiths versus Centaurs). Thus, the triumph of Pericles' fellow Athenians is a triumph of Greek over barbarian, a triumph of civilization over lack of civilization, and a triumph of people who embrace democracy over those who embrace a form of government that silences the voice of the people. These are values that we still hold dear today and I would suggest that this is one of the reasons why we still study these monuments and their associated art.
The works of the Periclean building programme is also considered the height of artistic idealism, harmony, proportion, symmetry, and rational control. A foundational value of Greek thought at this time was sophrosyne, which denotes a sort of balance within the human spirit ("moderation", if you will). Moderation is also a value for which we would do well to strive today.