The last lines tell us Gerry humbly joins the company of Homo Gestalt. Under Gerry, the gestalt behaved amorally—murderous and mean—for it had no society of similar beings from which to receive moral instruction.
Thanks to Hip, however, Gerry—and the gestalt—learns an ethic for a unique individual. It requires faith rather than obedience. Thanks to his emotional bond with Hip, Gerry places faith in the ethic that he should protect, inspire, and revere humanity rather than attack it.
That's why all the others who make up the rest of the Homo Gestalt species suddenly contact him via telepathy (Surprise!) in the very last pages. They'd blocked him off or put him in quarantine because he was too dangerous to everyone else. But now that he's learned Hip's ethic, they invite him to join their club, and now that he's a good guy, he humbly joins them.
This provides closure to the novel, because Gerry and his gestalt have now matured beyond its childhood formation stage under Lone and its vicious, murderous adolescence under Gerry to become an adult member of an advanced, truly good society. The Homo Gestalt society, we learn, guards all humanity, whether of the Homo sapiens or gestalt variety.
The ending also reveals some cool things about Homo Gestalt.They tell Gerry multiplicity is their first characteristic, meaning each is a diverse and discrete gestalt, but unity is their second, meaning they bond and belong together—no more of that loneliness that plagued the characters in Part 1. Homo Gestalt will let thousands die if it means millions might live, and they can't be corrupted because their faith in their social morality holds them together.
Sounds swell, right? The ending transcends the understanding of morals, society, and ethics we'd been given earlier in the novel. It leaves us with a new society, Homo Gestalt, with its own social morality. The very last sentence is Gerry, now humble, joining the new society. All's well that ends well.