In this paragraph, I believe that Berger is trying to say that the combination of emotions portrayed by the facial expressions, posture and positions of the subjects give the painting its value. In part of the third sentence,
“Terms like harmonious fusion, unforgettable contrast, reaching a peak of breadth and strength”
Berger uses a host of descriptive terms that require a lot of thought to uncover their meanings. It’s first important to understand what Berger explains is the consequence of using these terms.
“transfer the image from the plane of lived experience, to that of disinterested art appreciation”
This states that they change people’s view of the painting from an actual scene they’re witnessing to a fictional depiction of a group interacting. In other words, the terms expose the paintings as art instead of reality. When he says “harmonious fusion,” I believe he means that the positioning of the characters around each other creates a harmony of good-feeling among them that the individuals would not create on their own. Their facial expressions alone show a somber mood, but the paintings themselves show camaraderie and contentment. “Unforgettable contrast” means that the characters each appear to have different and complementary personalities and expressions. This instills a somewhat romantic feel into the paintings, meaning that it’s ideal but not realistic. The terms peak of breadth and strength signify that