You're correct that repetition is characteristic of epic poetry. This stylistic device serves several purposes:
1. references to the war remind the reader/listener of the brave exploits of the Greeks, specifically Odysseus, in the Trojan War;
2. the omens foreshadow the inevitable bloody doom of the suitors;
3. re-tellings of the story of Agamemnon's betrayal by his wife Clytemnestra and her lover Aegisthus serve to contrast sharply with Penelope's faithfulness during the all the years that Odysseus has been gone from and his return to Ithaca;
4. references to the gods are a reminder of the important role that the deities played in the lives of the Greeks who believed that their gods could take human form and walk among them for a variety of reasons;
5. repetition made memorization and recitation much easier for a traveling bard or musician to sing or recite this lengthy work, which was apparently presented one book at a time.