Symbolism, Imagery, Allegory
When Jacob visits Geertrui in the nursing home, she asks him to read a poem to her by Ben Jonson. We're not sure why, but we know it's important to her. The poem goes like this:
It is not growing like a tree
In bulk doth make Man better be;
Or standing long an oak, three hundred year,
To fall a log at last, dry, bald, and sere:
A lily of a day
Is fairer far in May,
Although it fall and die that night—
It was the plant and flower of light.
In small proportions we just beauties see;
And in short measures life may perfect be.
Symbolism alert: this poem is important to Geertrui because of all the memories it brings up for her. Check out the way she's described when her Dutch grandson reads the poem: "Geertrui's head turned and her eyes were on him again, intense, devouring. He had never seen the poem before" (12.59). In short, she eats it up.
Geertrui and Jacob read poetry from Sam's book to each other all throughout the war, but for whatever reason, this poem becomes the symbol of their love and passion for one another. Did you notice how the poem talks about the perfect things in life not lasting? Or how it tells us that even though the flowers are beautiful and fair, they die in the evening? The poem is really telling us that everything in life that is worth looking at or experiencing is only short-lived—you know, like Geertrui and Jacob's relationship.
Before Jacob's death, however, he and Geertrui are living through a war. People are dying all around them and life as they once knew it is actively being destroyed, so it's no wonder they want to cling to a poem about how great the beauty is in small and fleeting things.
We can think of life as they've known it as a tree—society and such as been built up over long periods of time, and when it falls there is little beautiful about it (just like the "dry, bald" log in the poem). But the life Geertrui and Jacob's love infuses their experience of wartime with, we can see as the day lily—bursting forth, though it's death quickly approaches—as an insistence on beauty no matter what happens in the world around them. Looked at this way, there is almost something defiant, and certainly something brave, to Geertrui and Jacob's love.
We later learn that Geertrui read this poem over Jacob's grave after he died. She tells us:
[…] at dusk I went out alone, and stood by Jacob's grave, and recited one of his favorite poems from Sam's book, an ode by Ben Jonson. He liked especially the last two lines, which he said summed up life better than any other words he knew. (17.66)
After Jacob's death, the poem takes on double significance. It's no longer just about living life to the fullest, war or not—now the poem also comes to represent Jacob himself to Geertrui, since it was one of his favorites. It represents everything they had together that was taken away by the war—and the perfection of their love for each other anyway.