拈来的长诗为落款的情书
[niān lái de zhăng shī wéi luò kuăn de qíng shū]
This translates roughly to 'A long letter in poem form that has been penned to seal love missives'. It refers to the writer picking lines spontaneously from poetry to sign off heartfelt love letters, reflecting romance and depth, and the artistry of expression in Chinese culture.