Part of Fiddler on the Roof that contains the musical number L’Chaim, which starts at 3:37. I will indicate time as given by the video.
The L’Chaim number in Fiddler on the Roof is composed of three phases which are rather obviously meant to be seen as such. These phases follow the classical dialectic structure:
Thesis (3:37-4:53) The Jews celebrate the announcement of Lazar’s wedding to Tzeitel, starting with singing and fluidly transitioning to dancing.
Antithesis (4:54-6:26) The Christians/outsiders sing, and then dance, a response to the thesis.
Synthesis (6:26-8:48) The Jews are assimilated into the Christian/outsider paradigm.
The cinematography, singing and dancing throughout is perfectly coordinated to construct these three phases and their meaning relative to the rest of the movie. I believe that they are actually meant to be a summation of the movie itself, and follow the general storyline: first we observe the Jewish community in relative isolation, then we observe the effects of outside intrusion (in the forms of Tevye’s daughters’ weddings as well as the threats of pogrom), then we observe the forced assimilation of the Jews as they are forced to leave their town and emigrate.
The thesis is not particularly thematically interesting, but the antithesis deserves particular examination. First, it should be noted that the Christians are all wearing very similar clothing, which brings to mind some kind of military uniform, echoing the pogroms (the lead singer also wears a military-looking cap).
5:00-5:08 This is an absolutely masterful reveal. But apart from that, we see that the Christians start off hanging back from the main dining area, but progressively move forward.
5:24 In response to the line “may we live together in peace,” Tevye answers “thank you” and starts to bow, but a fellow Jew holds him back. All through the antithesis, Tevye is held back and prevented from “fraternizing.”
5:25-5:32 The Christians begin to “advance” in earnest. Their song is friendly but their gestures and body language look vaguely menacing. At 5:39 look how the lead singer does a closed fist gesture which out of context looks aggressive.
5:45-6:26 The Christians start dancing within a circle. The cinematography no longer portrays the two groups as confronting each other, and instead makes it appear as if the Christians have completely taken over the floor, although this is not really true.
This is where the synthesis begins, and Tevye is no longer held back. The Christian bumps into him, apologizes, then holds out his hand. When Tevye has to take a decision during the movie, he always hesitates, thinks of traditions and has one-sided conversations with God. He likewise hesitates at 6:48 and looks back to his fellow Jews for advice. But no one is holding him back this time, and being happy and drunk, he takes the Christian’s hand and is taught how to dance in their style, which is actually similar to what you see at the beginning (compare the hand-slapping in 7:08-7:23 to the hand-slapping in 4:38-4:50).
Tevye provides the bridge between the self-isolated Jews and the outsiders; in the number he does so willingly because he is happy and drunk; in the movie he also represents the transition from isolation to modernity but does so unwillingly. In either case the result is the same. Lazar, on the other hand, is unwilling to participate in the dance, which corresponds to his status as the side of tradition against the other grooms who represent the “modern ways.”
If you look at the dancing in the synthesis in 8:16 on, you observe both types of dancing simultaneously, and alternating passages from both parts of the song. So the movie here is in a very obvious way telling us that this is a synthesis. At 7:43-7:50 we get another idea of a struggle or battle as lines advance and retreat with the dancing. At 8:27 the lines reform into circles, and it appears as if the Jews are dancing in a circle within a larger circle of outsiders; I think this provides a symbolism of the isolated Jewish community being surrounded by outsiders.
I think L’Chaim was intended as a microcosm of the movie as a whole, in the same way that many Broadway musicals have a ballet sequence in the middle that describes the play as a whole. It is meant both as a song with textual content and as an interpretive dance with its own conceptual content.