What oath does Achilles swear? Why does he withdraw from battle in the iliad?

In the "Iliad", Achilles takes an oath in the name of the scepter that he would not come to the aid of the Achaeans (Achaians).

Swearing by the scepter binds him to his oath as the scepter represents his respect for authority and his belief in the Divine. Achilles says that as the wood in the scepter will never again grow, he will also not continue to bring forth new growth for the Greeks.

The scepter represents the justice of Zeus.

Agamemnon agrees to return Chryseis to Chryses, her father and a priest of Apollo's temple. To compensate for what he believe is his loss he decides to take Achilles's captive, Briseis, as compensation. In response, Achille feels dishonored by Agamemnon. He refuses to fight for Agamemnon and withdraws from battle and decides to go home.

Grand Valley State University offers a guide to reading the "Iliad".

Of interest, Boston's Museum of Fine Arts has reorganized its Greek ancient art collection by theme. There are three galleries, with the first dedicated to Homer. Find out more from The Wall Street Journal.