This text is from The Children's Bach by Helen Garner.
In the street there was a dusty summer wind, a morning not quite hot enough. If they walked shoulder to shoulder, if they sat side by side, it was in order to become the world’s audience instead of being obliged to perform their personalities for each other. They bought tickets, they travelled. Their mutual curiosity was intense, but oblique. They watched one another witnessing the world: how two fat businessmen examined as merchandise the girl who pouted and pretended to read the paper in the café window with her skirt up round her thighs; how the waitress in Myer’s mural hall crossed the vast room with both arms high above her head and a dirty tablecloth hanging from each hand; the hippy boy on the tram who bought a ticket to St Kilda and announced to the other passengers, ‘I must go to the sea. To the ocean’; the girl whose lips moved as she read a book called Tortured for Christ. The world divided itself for them, presented itself in a series of small theatrical events. ‘Now,’ said a woman to a man at the busstop, ‘I’ll tell you the whole story. See the thing was that . . .’
What was the thing? They pointed out these eventlets to each other. They did not discuss or pass judgment, but defined themselves against the attitudes revealed by the unwitting characters in these dramas. They wanted to know each other less than they wanted to agree. Harmony! To be each other. They examined clothes in shop windows.
Does the whole part in bold mean: "they compared their attitude with other people's attitudes and knew themselves better, and because they wanted to be friendly (to be in harmony) they did not want to know each other very well"? Maybe in this case they came across some differences that made their relationship cold. They need harmony to be with each other