Half an Hour by C.P. Cavafy   In C. P. Cavafy’s “Half an Hour,” the short, late sentence translated by Edmund Keeley and Philip Sherrard as “That was very necessary” may seem more like a continuation of the poem’s terms than a turn from them. It lacks the lofty twist of the third sentence’s “But we who serve Art,” and its shift from narration to commentary is nothing new (“It’s sad, I admit,” Cavafy writes with similarly affecting reticence in the fourth line). What’s different about “That was very necessary” is that it both sums up the poem’s earlier scene—not only responding to it, as part of the narration, but compressing the narration into a single phrase—and sets up the explanation that follows. The…