Leo Marks's poem "The Life That I Have," read as part of Chelsea Clinton and Mark Mezvinsky wedding ceremony, seems on the surface to be the perfect wedding poem. It's straightforward and employs simple language--easy for the guests to understand and appreciate with one listen--and it comes across as genuinely emotional with its incantatory and almost pleading repetition of "yours and yours and yours." Here's the full text of the poem:

The emotion behind the poem, it turns out, was genuine and intense. Marks wrote it on Christmas Eve in 1943 for his girlfriend Ruth, who had just died in a plane crash. In his 1998 memoir "Between Silk and Cyanide," Marks wrote of the poem's purpose, "I transmitted a message to her which I'd failed to deliver when I'd had the chance."

That's heartbreaking enough, but there was more tragedy to come. When Marks wrote the poem, he was serving as chief code breaker/cryptographer for Winston Churchill's famed Special Operations Executive, the group tasked with encoding allied messages and cracking German codes. A mathematical genius, Marks reportedly cracked Charles de Gaulle's personal cipher during a spare moment on the toilet.

When Marks joined the Special Operations Executive, it was common practice to use well-known poems as the ciphers for encoding messages. Marks found this appalling, as any Nazi with a book of British classics could crack the ciphers, so he took to using his original poems instead.

"The Life That I Have," Richard Hyfler noted in an article for Forbes Magazine, turned out to be an ideal poem to use as a cipher, with its "absence of the high-value Scrabble letters like 'z' and 'x' or words with double letters that make code easier to decipher." Marks eventually gave it to a beautiful, young agent with the French resistance named Violette Szabo to use as her personal code. Before the end of the war, Szabo was compromised then tortured and killed by the Nazis. Her travails, along with the poem, are remembered in a 1958 film called Carve Her Name With Pride. You can watch a scene from the movie below.

There's something beautiful and uplifting in seeing Marks' poem freed from its tragic context and put to its original use as a statement of love and devotion in such a public forum (Clinton and Mezvinsky were apparently unaware of the poem's history when they selected it). But perhaps now, we should remember the pain and the sacrifice tied to it.