As Dr. Iannis and Corelli try to figure out an appropriate substitute for a mandolin string, Dr. Iannis abruptly asks if Corelli is going to marry Pelagia. Corelli is taken aback. Dr. Iannis tells him that they'll need to go to Italy or America, though he insists that Pelagia will wither outside of Greece. Corelli says that he thinks things will be just fine with Pelagia; she's suggested to him that because Corelli is obsessed with music in the same way that Dr. Iannis is obsessed with medicine, she's already learned how to love someone like him and their nationalities are of no consequence.
Corelli's assessment of the reason Pelagia will be able to love him shows that Pelagia's ability to think critically is indeed something that Corelli sees as an asset, not a hindrance. Further, when he says that their nationalities don't matter, he indicates that he sees humanity as a group as being fundamentally the same regardless of where they live.
Dr. Iannis is touched but insists Corelli doesn't understand. He goes on to explain that all Greeks have two Greeks inside of them. The first is called the Hellene and is reasonable, loves education, and obeys the law. The other is called the Romoi and seeks power, money, and self-interest. The only quality the two share is a love of country, though the Hellene will fight humanely against threats and the Romoi is more like Mussolini. Corelli insists he doesn't believe that Pelagia has this horrible other side. Dr. Iannis says that he's just saying that they'd need to live in Greece. He leaves the room and returns to say that Greece has experienced nothing but slaughter for millennia and it's teeming with ghosts. He cautions Corelli that there will be more and he shouldn't make plans.
Dr. Iannis's final warning to Corelli foreshadows the horrors to come by insisting that history will repeat itself in Greece. This shows Dr. Iannis using his grasp of history to influence how he looks at his present and the future, as he recognizes that it's impossible for the war to end peacefully, even someplace like Greece that has little strategic importance. By giving Corelli his blessing in other ways, Dr. Iannis does show that he now fully accepts Corelli as a worthy person.