Mentre che la speranza ha fior del verde
– La Divina Commedia, Purgatorio, III
Thanks to the Princeton Dante Project, we are able to translate this for you. In English, the epigraph reads, "As long as hope maintains a thread of green." This is the last bit of a longer phrase, which is, "By such a curse as theirs none is so lost/ that the eternal Love cannot return/ as long as hope maintains a thread of green." (For more on Dante's Divine Comedy, check our Shmoop Guides on Inferno, Purgatorio, and Paradiso.)
It's not hard to see what Warren is getting at, whether you've read the Divine Comedy or not. This epigraph sends us a message of hidden hope, which we don't see much of until the end of the novel.
The "green" in the epigraph speaks to the kind of return to innocence that Jack finds when he learns the truth about his childhood. The love between him and Anne must have maintained "a thread of green" through all the trials and tribulations, though we can't necessarily say their love is eternal.
The third and fourth paragraphs of the novel deal with this theme explicitly, and provide a set-up that carries itself through the novel. To get to Mason City from the Capitol (presumably Lafayette, Louisiana), one passes a view of "red hills now, not high, with blackberry bushes along fence rows […] and then a place where the second-growth pines stand close together if they haven't burned over, there are black stubs" (1.3).
Then, Jack explains that, "There were pine forests a long time ago but they are gone. The bastards got in here and set up the mills and […] paid a dollar a day and folks swarmed out of the brush for the dollar" (1.4).
The "black stub" imagery is the key. We see it again when Jack creates a memory of the beginnings of the relationship between Ellis Burden and Mrs. Murrell. He says, "I have not seen the town [in Arkansas]. But I have seen the town in my head" (3.171).
The town where Ellis finds Mrs. Murrell is mill town and Jack imagines them walking together, out beyond the houses, where the stumps are located. Jack says he can "see them standing in the middle of the ruined land" (3.173).
So, we find out that Jack is a bit of an environmentalist. This is important in terms of his political profile. He thinks that there are more ways for people to make money than by milling forests. Jack's sadness over the "ruined land" is evident. But, being Jack he connects this to the larger issues of both the novel and his life. The ruin of the land parallels the ruin of the lands people. The aftermath of slavery has left the people like the "stubs." This is obviously very problematic language. But in Jack's mind, this is what slavery has done to the black people of America.
Jack thinks that the same lack of reverence for life that allowed slavery to occur also allowed the destruction of the natural environment. We aren't in any way implying that the burning of forests is on the same level with the treatment of slaves in the South. Still, it's important to notice that Jack (whether you agree with him or not) sees these two evils as springing from the same source.
Being Jack, he also connects this to his personal problems – i.e., the "black stub" of his past, the mystery of Ellis Burden and Mrs. Murrell. Before Jack knows the truth about them, he most closely associates them with the picture of "ruined land," and so too himself. Until he understands things, he sees himself as the messed up byproduct of a land of human and environmental disasters.
By the end of the novel, Jack realizes that, in America, "hope maintains a thread of green" and that with proper food, care, and love, the thread will do its best to grow, like "the second-growth pines," in spite of much adversity.