This is the first reference to a pet notion of Franz’s: “the Grand March of History” represents the narrator’s (and probably Kundera’s) ironic -- even sarcastic -- characterization of the illusions of Western leftist intellectuals. Franz believes in history as an ordered, and likely progressive, process -- ever onward, ever upward.
The concept will be mentioned casually several more times before the narrator discusses it in depth. When Franz and Sabina travel to Amsterdam, he thinks of the Grand March of History while looking at the Oude Kerk (see Bookmark for page 109). After Sabina leaves him, Franz’s student mistress takes up the notion as her own (section 11 of Part Three, page 126).
Only in Part Six, which is in fact titled “The Grand March,” will Kundera and the narrator address the concept in depth, in connection with socialist May Day parades and the horror of kitsch (of which the Grand March may be an example), culminating in the ironic, meaningless death of Franz from a mugging in Bangkok right after he has tried to participate in a literal march into Cambodia that is a comic parody of the Grand March he believes in.
In contrast, the narrator says Tomas and Tereza step out of the Grand March of History (or the illusion of it) when they head to the country with Karenin: “… I love Tereza with the mortally ill dog resting his head on her lap. I see them one next to the other: both stepping down from the road along with mankind, ‘the master and proprietor of nature,’ marches onward” (section 2 of Part Seven, page 290).