what is visionary value of Judth's letter?

This section is important because it clarifies and deepens our understanding of the relationship between Charles Bon and Henry Sutpen, and further clarifies our sense of Mr. Compson as a speculative, analytical thinker to whom everything is a sign of the predestined doom of men great and small. But this is also the most difficult section in the novel in some ways, because Mr. Compson's description of events is based on incomplete information, and is therefore misleading. As we will learn in subsequent chapters, Thomas Sutpen did not ride to New Orleans simply to investigate Bon, and did not merely discover that he was keeping an octoroon mistress or wife whom he also seemed to "own." Sutpen rode to New Orleans because he recognized Charles Bon as his own son, his child with the part-negro daughter of the Haitian plantation owner and Sutpen's first wife; if Bon married Judith, Sutpen's daughter would

Sutpen's daughter would be marrying not only a man with negro blood, but her own half-brother.

Mr. Compson is also wrong when he imagines Henry's confrontation with his father to be centered on the problem of Bon's mistress; the break actually occurred, as Quentin and Shreve later realize, when Sutpen told Henry that Bon was his brother. During their subsequent trip to New Orleans, then, Bon was unlikely to have worried much about showing Henry his mistress/wife; Henry probably would have taken her as lightly as Bon did. But Mr. Compson does not know at this point that Bon was Sutpen's son, or that Bon's mother had negro blood, and his analysis is limited by his lack of knowledge. He tries to construct a whole picture but cannot.

Faulkner does not mislead his readers simply to complicate his plot, or even to preserve the mystery surrounding the story. Part of his project is to show how the past is reconstructed by those who come after it, how the examination of the past is in some sense a creative act on the part of the examiner, who must provide motives, thoughts, and feelings for the people whose lives he examines. Mr. Compson reconstructs the past no more imaginatively than do Quentin and Shreve later, but his factual framework is based on less information. Furthermore, the reconstruction of the past in the individual's mind is dependent on the personality of the individual, and on the relationship of the individual to the past. So Rosa, who lived through what was to her a nightmare, can stew in her own bitterness for decades, constantly recreating Sutpen in her imagination as a demon from hell and an ogre; Mr. Compson, more distant from the events of Sutpen's life, can view the story as proof of the role of fate in human life; and Quentin, quite distant from the Sutpen story but still strangely preoccupied with it, can construct the most factually accurate version of the story, and then connect the story abstractly to the overall history of the fall of the South. But he also ranges further into speculation than either his father or Miss Rosa.