Nan Zhou's first chapter refers to Guan Ju, the first poem in The Book of Songs Nan Zhou, and Du Fu's three sentences refer to the third sentence of Du Fu's four happiness poems: Wedding Night. This is a traditional wedding couplet, which often appears on the doors of newlyweds.
Du Fu, Sixi
We met an old friend in another country after a long drought.
Wedding night, for the first time.