Let us remember first and foremost that Helen was the reason for the entire Trojan War, as her kidnap or escape with Paris, the young prince of Troy, was what gave Meneleaus and his brother Agamemnon reason for attacking Troy and starting one of the most famous battles in mythology. In Book 4, we focus on the fates of other heroes from the Trojan War, and Helen is one of these. Seeing her happily married to her original husband again, and what is more, celebrating the birth of her children, perhaps foreshadows the happy ending that is in store for Odysseus and his family when he finally makes it home and restores his position.
Let us also focus on the particular story that Helen offers about the father of Telemachus. As the characters feast in this book, Helen and Menelaus tell Telemachus stories that celebrate the cunning and ingenuity of Odysseus, and how this was used to win the battle. Helen's story in particular is noteworthy because she tells Telemachus how his father disguised himself as a beggar to infiltrate the walls of Troy and gain access to the city. Given the sheer number of times in this book when Odysseus either disguises himself or pretends to be someone he is not, witholding his identity, this story is key for preparing us for the character of Odysseus and the kind of stratagems he employs.